We know for a fact that Hitler hated atheists and the Nazis only recruited Protestants and Catholics. Probably this question is not too sincere anyway, however, I will use this opportunity to point out a common mistake.
“Atheist” is not an identity. It is a lack of religious identity and disbelief in God.
If Tom said “I am a Christian”, you would learn something about Tom, on the other hand, if Julia said “I am an atheist” you would get to know what she was not, rather than what she was. Hence Hitler’s atheism would be irrelevant even if he happened to be an atheist.