The first time I heard the claim “Hitler is an atheist” I was dumbfounded. Not only do some people in the US believe Hitler was an atheist but also they assert that the Nazi regime did what it did because it was an atheistic movement.
In reality, however, Nazis were predominantly Catholics and Protestants, Hitler loathed atheists, and claimed atheists were all communists, hence, where possible, he even got them killed.
I presume because the Nazi regime was killing Jews some Christian groups want to distance Christianity from the Nazis, and because they can apparently sell the “Hitler was an atheist” story in the US, they use the opportunity.
In his book, Mein Kampf, Hitler refers to Jews as an ethnic group. He goes on to say that by not allowing their men to marry non-Jews they make sure Jewish blood stays pure, and by allowing their women to marry non-Jews they poison the German blood. (There is no logic to this, of course. Because the children of Jewish women married to non-Jews are considered Jewish if anything, the Jewish communities worldwide have been “poisoning” their own blood all along.)
The fact that Hitler believed in God, and the Nazis were Christians do not say anything about Christianity either. Nazism was neither a religious nor an irreligious movement. Hitler had Jewish communities massacred in Germany and German invaded lands for their ethnicity, not their beliefs. Therefore the entire discussion of if Hitler was a Christian or if he actually disbelieved God is not meaningful.