Assuming that by "God" you mean an omnipotent, benificent and all-knowing supernatural entity, this question boils down to a rephrasing of the classic problem of "evil". And I think it was argued by Epicur quite sufficently thousand of years ago:
Is God willing to prevent evil, but not able?
Then he is not omnipotent.
Is he able, but not willing?
Then he is malevolent.
Is he both able and willing?
Then whence cometh evil?
Is he neither able nor willing?
Then why call him God?
So in order to get out of this dilemma while still upholding such a god concept, one has to rationalize evil differently.
You can ad hoc rationalize why man is to blame quite easily: Simply invent "sins" committed by man, so that blame can be attributed "correctly". Just watch the news of any natural disaster, you surly will find some theologian claiming that the wicked way of man made that event a just and rightful punishment.
Problem is, the concept of "sin" only works a theological framework that allows for "free will". Not only is "free will" incompatible with the physical world, it also conflicts with the all-knowing attribute. Surly such a god would know how his creation would choose.
The whole "sin" concept has also troubles with the disconnect between what humans think to be good and a god as origin of "goodness". As in the end, whatever god wants to be "good" would be good. Even murdering millions of people. This is why you could even turn this whole argument upside down by arguing that a god was there the whole time during the holocaust as it very much wanted the holocaust to happen to punish the Jews!
How benevolent such a god would be is debatable. For me, it would be a malevolent one, but I am not the standard here. If God would want it, it would be "correct". Anyone else would have gotten it "wrong".
Nazis did not consider themselves doing evil acts. They did what they thought to be right. In their twisted world view, Jews were parasites, and it was their duty to destroy them. "Gott mit uns" aka "God with us" was one of their mottos.
And as cruel as that may seem, there still are many irrational conspirational theories attributed to the Jews, and to this very day some people think it is their holy duty to purge the Jews from this planet. And not because they consider themselves evil, no, but because they think they are the good guys as strange as that may seem.
Or as Voiltaire once said: People believing absurdities will commit atrocities.
In the end, I would claim there is no sufficient enough argument that would support the concept of a benevolent god and the event of the holocaust. Playing devil's advocate (Pun very much intended) is a fool's errand here.