Hitler's beliefs are difficult to know, although he grew up catholic and was definitely steeped in religious culture. His speeches and books draw upon religion and make overt statements of his own religiousness and expectation of God's blessings.

He also complained about religion and made other statements that muddy the waters. So, it's not clear that he was an atheist, and he certainly publicly and proudly claimed to be a believer doing God's work in the world. However, even if he were an atheist, he clearly held a worldview that was primarily informed by religious themes and ideas. I mean, he hated the Jews. The JEWS. He vilified the enemies of his catholic upbringing! Can't get much more religious than that.