You can look at 'the Holocaust' and 'the Church' and a very complicated picture forms. So the first of your two questions is terribly broad. Hitchens account is not in contradiction with your other source, he just chooses to polemicise in leaving out some aspects and emphasizing the bad.
The Catholic Church formed Hitler's belief system to a large part, had rampant anti-judaism – until Nostra Aetate – to show in itself, but as a whole not so much more anti-semitism as was prevalent almost everywhere, formed a Reichskonkordat with the nazis and so was helping to stabilise the regime.
On the other hand some priests were very vocal in public in opposing the persecutions, also of the Jews, and many catholic organisations were actively hiding Jews. Do not misread "many" compared to the numbers killed but in relation to a widespread view that absolutely no German had compassion. "Many" in this regard remains still much too few.
The church itself was persecuted to a certain extent and the Pope played quite a bewildering part during the whole time. Not really silent in public, but also not saying much. Not really doing nothing, but doing much too little.
It seems that the majority of scholars say that the documented acts of successful resistance, and open resistance, of parts of the Catholic church is proof that the lack of much more widespread resistance has to be seen largely as an enabling factor in the holocaust. Only the fact that some did resist and risked quite a bit in the process was able to keep the church from completely loosing its face.
That protest and opposition was still possible, and that the church might play quite a significant role in such protests, actually ending a large scale killing programme can be seen in how they handled the "dress rehearsal" for the holocaust: the Aktion T4. The later term "T4" was codenamed Aktion Gnadentod (operation merciful killing) at the time and stood for killing "unworthy lives", that is a murderous eugenics programme for people with disabilities etc.
In 1943, Pope Pius XII issued the encyclical Mystici corporis Christi, in which he condemned the practice of killing the disabled. […] On 24 August 1941, Hitler ordered the suspension of the T4 killings. After the invasion of the Soviet Union in June, many T4 personnel were transferred to the east to begin work on the final solution to the Jewish question.
(From: Wikipedia – Aktion T4 – Opposition)
Michael Phayer: "The Catholic Church and the Holocaust, 1930–1965", Indiana University Press: Bloomington, Indianapolis, 2000.
Dan Stone: "The Historiography of the Holocaust", Palgrave Macmillan 2004
: Basingstoke, New York, 2004. (Ch. 13, Robert P. Ericksen & Susannah Heschel: "The German Churches and the Holocaust", p 296–318.