What nonsense.
If Hitler murdered people for "religious reasons," why is it that Jews who converted to any other religion were killed the same as any other Jews? And what kind of "religious reason" motivates someone to kill Gypsies? (You'd maybe like to cite a long history of Christian anti-Gypsy-ism?)
If Hitler was murdering Catholic Poles by the millions -- and he and his pals were very clear that Poles were ultimately to be exterminated, and almost as many Poles were killed as Jews -- then what religion motivated him to do that? The religion of "Anti-Polishism"? "The Church Of Ubermenschen Who Hate Polacks"?