To address the account you provide. It presents strong cases on both sides. But I'd not two distinctions: The case that Hitler was anti-Christian is based on private statements, and later statements. The case that Hitler was Christian is almost exclusively based on public statements made by Hitler during his rise to power. I have to agree with what is sort of a conclusion to that account:
"It seems Hitler, like many modern-day politicians, spoke out of both sides of his mouth... Also, it seems probable that Hitler, being the great manipulator, knew that he couldn't fight the Christian churches and their members right off the bat. So he made statements to put the church at ease and may have patronized religion as a way to prevent having to fight the Christian-based church. "
To state what the author seems hesitant to: Hitler played the Christian a little early on, while rising to power. Once firmly entrenched, he played the anti-Christian.
And I will disagree with your source on some points: He states that many of the leaders of Germany were devout Christians. I would challenge him, if I could, to name one regular communicant. Likewise, he claims that Hitler never left the Catholic Church. He did not receive communion as an adult, and unlike many lapsed American Catholics, he knew very well that by failing to receive communion, he was rupturing his ties to the Catholic church. How else do you expect him to leave? Do you want him to APPLY for a formal excommunication? Burn his baptismal certificate?
I would contemplate one distinction where Hitler's nihilism may not be consistent with atheism: He does seem to subscribe, in some speeches, and in some ways which may not be mere deceit, to some notion of a god. Perhaps he has elevanted Nietzsche's will to power to a deity; perhaps he is that god. But while such references may be no evidence of "religion" per se, they may be refutation to the disbelief in any entity called a god. It's hard to separate belief from propaganda with Hitler, but he may even have had some Caesar-like notion of divinity.
Ideologically, however, where Christianity has many specific and universally accepted notions which are emnity between Christianity and Nazism, there is plainly nothing in atheism to oppose Nazism. That's not saying that there aren't personal ethics held by atheists that don't hold Hitler's actions abhorrent.
There is nothing in the theory of universal gravitation to oppose Nazism either. I don't believe in a god. Why should that bear on any political movement? Some Christians undoubtedly supported Hitler. The Serbs loved him; he let them impose orthodox Christianity on their neighbors. Others opposed him. It appears they're in the same boat I am.
What is there in Christianity to oppose Nazism?