The truth is, though, is that it is not really clear if Hitler was in fact an atheist, or even a Christian. Richard Dawkins, in the God Delusion (pg 272-78), lists specific examples where Hitler seems to be anti-atheist and pro-Christian. In a speech in 1933 Hitler declared a fight against the atheistic movement, and claims to have stamped it out. In another speech in 1922 he repeats several times that he is a Christian. Then there is his famous quote from Mein Kampf:
Hence today I believe that I am acting in accordance with the will of the Almighty Creator: by defending myself against the Jew, I am fighting for the work of the Lord.
However, there are other references (see here) where Hitler expresses anti-Christian sentiment. For example, during a private conversation on the 19th October 1941, Hitler was recorded to have said the following:
The reason why the ancient world was so pure, light and serene was that it knew nothing of the two great scourges: the pox and Christianity.
Moreover, Hitler heavily persecuted members of the Confessing Church; the theologian Dietrich Bonhoeffer, for example, was hanged in a concentration camp in April 1945.
So Hitler's religious beliefs are not as certain as some apologists, or even some atheists, would have us believe. My own view on the matter is the same as the one put forward in this article: that Hitler's 'god' was not the Christian god, but rather the German national identity. This is what he worshiped, and he persecuted anyone, atheist or theist alike, who did not do the same.