You might question why he was fine being surrounded by mystics and neopagans who hated Christianity, why none of his private statements about his supposed religion were positive or why he never attended Church for non-ceremonial purposes in his adult life.
You might even point out that Hitler rejected the entire old testament, thought that Paul was a lying jew who corrupted the original Aryan teachings of Christ, and believed that Jesus wasn't even divine.

But don't worry, Hitler wasn't actually opposed to Christianity, he just dislike CATHOLICISM you see! Just standard prot stuff really, not that different from american evangelicals when you think about it.