I'm not sure the Yugoslavian military were ever actually combatants"combatants" in the Angolan Civil War in the strict sense of the term. I was living in Southern Africa when the war broke out and so I've read quite a bit about what was going on in Angola.
The military support for the MPLA came from Cuba, together with a number of Russian specialists (although it is possible that Yugoslavia did sent some specialist military advisers to assist the MPLA and Cubans).
I do know that Yugoslavia was one of the countries that provided financial and materiel assistance to the MPLA before the civil war actually broke out in 1975. They may even have provided military training before 1975 (although I thought that training was provided by the USSR). On page 519 of Into the Storm: American Covert Involvement in the Angolan Civil War, Shannon Butler observes:
what little information is available indicates that the bulk of the weapons and military equipment came by ships, most of which were neither Soviet nor even Soviet-bloc. In fact, during these critical early months of 1975, Yugoslavia seems to have been the MPLA’s main supplier, and it is highly doubtful that the independent and non-aligned Yugoslav’s were doing Moscow’s bidding.
Further,
The MPLA admitted that “some” Soviet weapons and equipment arrived during this time frame, but “they were of lesser importance” to that delivered by Yugoslavia. MPLA leader, Paulo Jorge iterated the importance of Yugoslavia’s support for the MPLA during this time frame.
But there is no mention of Yugoslavian "boots on the ground".
Full text of Into the Storm: American Covert Involvement in the Angolan Civil War, 1974-1975 by Shannon Rae Butler on the Internet Archive.