Most Germans would consider themselves Christians because "All Germans are Christians, aren't they?" Doesn't mean a thing what mom and dad were, if you dont believe and follow the teachings of Christ, you're not a Christian.
Additionally, the Church had (has) a special relationship to the German State (and in other European states), much like the Anglican Church in England. There is no genuine "separation" of Church and State - meaning no offical State Church - as in this country. Taxes subsidize the official Church. Clergy are State employees and people who are registered "christians" receive wedding and burial privileges given only through the Church. Otherwise, they have to pay for them even though they were already taxed for them.
So, being a "christian" in many European countries means something other than being a Christian (in the actual sense of the word). Therefore, no doubt many of the Nazis were "christians" but not Believers; most people were (and are) "christians" in name only. If you will remember, Hitler made great efforts to subvert the State Church and make it subservient to Nazi State doctrine and policy - and he was by and large successful in turning the State into an accomplice (if only a passive one) of the Nazi Party, much like the Soviets did with the Russian Orthodox Church.