I am somewhere on the net defending the notion that Nazi Christianity isn't really that strange in the grand scheme of things.
The Gnostics are a very early heretical branch (in this context meaning only that they didn't win) even pre-Trinitarian. They make up about 0% of Modern Christian thought. And while a lot of the early groups did actually vote as to whether to keep the OT or not (with some outright rejecting it), it was generally accepted by the winning branch which became the Catholic Church and then the Catholic and Orthodox church and later gave rise to the Protestant groups.
The better example would be the many groups of real Christians who argue that Jesus fulfilled the law and that with Jesus the law was super-seceded and no longer needed. Though these individuals cite Paul who apparently was, according to Nazi theology, a horrible snake who corrupted Jesus' true stance against the Jewery. And, as it turns out they simply didn't. They accepted the OT.
I have heard that they invented a pseudohistory by which modern Jews are not ancient Jews. Though, I don't have a reliable source for that. And they certainly did that for Jesus, by accepted the whole 'bin Panthera' story that was made up and written into the Talmud and repeated in some pagan sources (Jesus was the kid of a Roman Legionnaire, not born of a virgin!) The Nazis took that as true and said, see he was a member of the Master Race.
They didn't reject the OT.
Hitler for example in the Table Talks compared himself quite favorably with Moses.
"I have never found pleasure in maltreating others, even if I know it isn't possible to maintain oneself in the world without force. Life is granted only to those who fight the hardest. It is the law of life: Defend yourself! "
"The time in which we live has the appearance of the collapse of this idea. It can still take 100 or 200 years. I am sorry that, like Moses, I can only see the Promised Land from a distance."
A side note, of importance, for a variety of reasons (mostly due to a French conman) this is translated in the only full English version of the Table Talks(Roper) as:
"Our epoch will certainly see the end of the disease of Christianity."
Which any check to the actual German would dispossess that notion.
But, they also used the OT as an example of good laws, namely laws based on race:
"I have written such articles again and again; and in my articles I have repeatedly emphasized the fact that the Jews should serve as an example to every race, for they created the racial law for themselves-- the law of Moses, which says, "If you come into a foreign land you shall not take unto yourself foreign women." And that, Gentlemen, is of tremendous importance in judging the Nuremberg Laws.. These laws of the Jews were taken as a model for these laws. When after centuries, the Jewish lawgiver Ezra demonstrated that notwithstanding many Jews had married non-Jewish women, these marriages were dissolved. That was the beginning of Jewry which, because it introduced these racial laws, has survived throughout the centuries, while all other races and civilizations have perished." --Julius Streicher (Trial of The Major War Criminals Before the International Military Tribunal, Nuremberg, 1945, Vol. 12)
The point is, while it seems really odd, it's not actually outside the even pretty narrow band of Christian thought of straight forward Protestantism. Without needed to go back to Arianism or Marcion or any of the heretics, which I would actually have to agree deviate pretty markedly from the Christianity that survived the Dark Ages.