I once saw a lecture by a Black German who had lived through WWII. He was the son of a German missionary father, and an African mother. The Nazis went after the "Rhineland Bastards", children of Black French post-WWI occupying soldiers and German women, but mostly ignored Black Germans like him. He was rejected from military service, which killed many of his friends, so he actually did better for being Black.
He came to the USA as a German reporter after the war, and for the first time in his life was denied entry into government buildings, use of public facilities, and even the right to ride on a bus where he wished. Interesting how that works.
I do believe the Nazis would have sooner or later realized there were a few Black Germans, and killed them all.