I have heard this claim, usually by antagonists of the Gospel of Jesus Christ. When confronted with an element of truth, this statement will come up many times, by these people.
Were the Nazis really Christians though? Perhaps that depends upon your definition of Christianity. If you think Christianity means belonging to a Protestant or Catholic church, then your understanding of Christianity would be much like a club member belonging to a club. Only the club is called, 'Church'.
If your understanding of Christianity is based upon a profession of faith, it could be a little closer, but still not close enough. If a person professed to know or believe something, then that person has to be informed on the object of their faith. In other words, a person who professes to know Jesus Christ as Lord and Savior, yet lives a self-centered life with the belief that God is ok with that, doesn't really understand what Christianity is all about.
Christianity is about the Gospel (good news), and the Gospel is the crux of the theme of the Bible. In the Beginning, God created man perfectly. Man was tempted to sin, and the whole human race was ruined. The disease of sin entered in. Death was the result. But God intervened by sending His Son, to live a perfect life, and to die in our place, for our sins. Because of that Death, we can go free and be fully forgiven of our sins. When we repent and come to Christ, the Bible says we are born again. We now have the power to live a holy life, because God's Spirit dwells inside those who know and love God.
Anyone can profess to be anything. People believe what they want to believe. People also think they can twist God's arm and make Him do for them what they want Him to do. We think we can pull the wool over God's eyes, because we rebel against Him, yet He doesn't kill us. We have lost our fear of Him, because of His mercy.
The Bible says 'By their fruits you will know them'. If God is holy and pure, and if a person is a true Christian, according to the Bible, he or she will become more like Christ. God is love. A person who knows God grows in love for God and for other people. Other people are treated with kindness and respect. Only the proud, hateful people are the ones who bully people around. Pride, hate, trying to control others is not a trait from God. Those who manifest those qualities are not true Christians, according to the Bible. In fact, they are under God's Judgment.
I am not sure why people say that Hitler or the Nazis were Christians. There is nothing in them that looks like Jesus did. They are not following Jesus in His example. Neither are they bearing any kind of good fruit in their lives or activities.
Jesus said, 'Not everyone who calls me Lord will enter into the kingdom of heaven'. I don't think Hitler even called Jesus Lord. He was raised in a Catholic church, and went to Catholic school, but his teachers were not impressed with his art work. I don't know that he even stayed with the Catholic church or not.
The only thing I am aware of that ties Hitler with God would be the belt buckles they wore. Supposedly, engraved on the belt buckles were the words, 'Gott Mit Uns' which means 'God with us'.
So, tell me how a belt buckle confirms someone as a Christian. Anyone who uses this argument has a very weak argument. It is about as absurd as those who would say that the Holocaust never happened.
Even if Hitler did profess to be a Christian, his life betrayed him. The real person is shown by his or her actions. Actions manifest what is in the heart. Hitler wanted control. He wanted lots of control. But the Bible says that we are to serve other people instead of trying to be authoritative over them.
Hitler's life did not show the love of God. Hitler's life was full of hate and pride, the things that God opposes so much.
You don't have to buy into the lie that says that the Nazis were Christians. We are mature enough (hopefully) to be discerning to know what is real and what is not, what is true and what is false.
Discerning what Hitler was, is not hard. Don't let anyone trick you into an argument against Christianity using the Nazis as an example of Christianity. It just aint so.