Does anyone with any relevant expertise know the general mood of the armies during the time? Is there documentation of any concerns from high ranking Soviet military officers, or of their Warsaw Pact counterparts, as to the reliability of Warsaw Pact allies in the event of a military engagement with NATO during the 1980's?
I have found a source, "Intelligence Estimates of the Warsaw Pact" from "Studies in Intelligence Vol. 51, No 4 (Extracts-December 2007)", which is an academic paper that covers Western intelligence estimates of the reliability of Non-Soviet Warsaw Pact forces. Fortunately, it also contains several quotes from Warsaw Pact Generals.
It covers estimates from the late 1940's/early 1950's through to the end of the cold war, and tracks how the Western intelligence community perceived the reliability of NSWPs.
It frequently mentions that the military reliability of NSWP forces varies depending on the country, and the event in question as well as the nature of the conflict they are involved in. For example, the below quote covers a 1977 estimate regarding the issues the Soviet Union was facing within Poland at the time and it concludes that the Soviets could not have confidence in the reliability of the Polish military in resolving the issues.
A June 1977 assessment, "Probable Soviet Reactions to a Crisis in Poland”, concluded that Moscow would first search for a nonmilitary solution in addressing labor unrest and political dissidence: The Kremlin, it asserted, recognized that an invasion of Poland-with its much larger population of intensely nationalistic and anti-Soviet people- would pose much more serious challenges than those faced in Czechoslovakia. Any intervention would with near certainty, "be met with widespread and bloody opposition, including some from elements of the Polish army." Although the assessment varied some over the next 4 years, the IC remained confident in it's judgement that Moscow could not count on the Polish military for much assistance in resolving it's "Polish problem"
Page 9, Middle Column
Further on, the article quotes from a 1983 intelligence paper entitled "Military Reliability of the Soviet Union's Warsaw Pact Allies" regarding NSWP reliability and compliance in a war with NATO. It concludes that it is likely that they would be initially reliable but this could change as the conflict evolved.
"We believe that the Soviet orders to go to war would be successfully be transmitted from the Soviet General Staff to NSWP line units that would, in the main, obey these orders at least in the initial stages of a conflict with NATO. However, we also believe that NSWP military reliability would be degraded by a static front, and substantially degraded by Warsaw Pact reserves"
Page 10, Right Column
According to the paper, the intelligence communities final thoughts on the reliability of NSWP forces were delivered in a National Intelligence Council memo in April 1990 - "The Direction of Change in the Warsaw Pact"
Recent political events in Eastern Europe will further erode Soviet confidence in their allies. Moscow cannot rely upon Non-Soviet Warsaw Pact forces; it must question its ability to bring Soviet reinforcements through Eastern European countries whose hostility is no longer disguised or held in check.
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Fortunately, the paper then continues to assess the truth of the intelligence communities assessments of NSWP forces saying that
Most academics came to the same conclusions as the IC did on NSWP reliability. After surveying 59 former Easter European servicemen and conducting exhaustive research, A. Ross Johnson and Alexander Alexiev asserted: "This study provides empirical support for earlier studies concluding that the USSR can rely on NSWP forces - but very conditionally"
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The paper then continues in it's assessment with quotes from Soviet commanders, for example in one section it states that Moscow's assessment of the reliability of it's allies was more pessimistic than the Wests mentioning that the memoirs of Col. Oleg Penkovskiy repeatedly mentions Soviet concerns about East German forces.
Penkovskly, for instance, cited Gen. Kupin, the Commander of the Soviet Tank Army in Dresden and others stationed in East Germany as asserting that
“in case of a Berlin crisis or a war we would have to kill both West and East Germans. Everything is ready to fight against not only West Germany but East Germany as well, because the Germans have Anti-Soviet sentiments”
Page 12, Right Column
So, to answer your question "Is there documentation of any concerns from high ranking Soviet military officers, or of their Warsaw Pact counterparts, as to the reliability of Warsaw Pact allies in the event of a military engagement with NATO during the 1980's?" The paper I have found (and linked to) lists several sources and indicates that both the Western Intelligence community and Moscow, as well as other WP nations, believed that NSWP forces would not be totally reliable in the event of conflict.
To be honest, I've just read through most of the article and quoted parts that I feel are relevant to your question, but you will get a much better, and much more in depth, answer to your question by reading the article I have linked to.
Your question is very broad, as it concerns large territory, and this is difficult to answer how large morale was. Even if eg. soldiers did not want to fight, we don't know how would they if they had to. In my opinion it is then a kind of a "what if" question.
As I understand my answer is not what you expect ("documentation") I can share my notices from talks with people who served in the army in that time (birth date 1950s.), but we must remember it is not a valid historical source, first because people tend to remember mostly good things (it was 30 years ago!), then it was only in Polish conscription force (so they were no professional soldiers), and last not least I know only few of them.
Since its creation the Polish state had very large respect to army and this had not much changed after 1945. I remember that Milicja (Polish police) was hated, but the army not; even during the Martial State. Writing this I mean ordinal soldiers, not generals like Jaruzelski.
The people whom I know and who was recruited do usually think this time was wasted, but not totally. There were some possibilities to learn something, like vehicle repairing or passing a driver license exams, but in many ways it was fulfilling stupid orders, that did not make sense -- but this might be in any army in the world. There were also some Polish sayings about positive effect of the military service, and not being in the army (if you were not an anti-communist or sick) was considered some kind of shame.
Nevertheless, I'm sure that Polish army would fight with high morale, if it was attacked. I think the patriotism and strong nationalism would make them fight NATO, but -- if there were no Martial Law but a Soviet campaign -- the Soviets as well. Some people in Poland claim that there was no possibility of a Soviet intervention these days as the USSR was busy in Afghanistan, and they were afraid of losses, because they were sure that all Polish nation would stand against them, so Jaruzelski should be considered a traitor (he assumes that he made the Martial State because he did not want Soviet intervention). There is large documentation about Martial Law, however the discussion is not still concluded.
Some years ago there was a tv series about Marian Zacharski, who was considered by the Polish maybe not a hero, but some person that we could be proud of. The only problem was that the information he stole was passed to the Soviet Union, and not to Poland. Many people consider Ryszard Kukliński a traitor, but many are proud of him as well.