I don't disagree with you about the art of prostitution and prostitution for art's sake. And maybe for money. Perhaps it is just a matter of degree, but perhaps it is an important degree in the case of selling Hitler.

"You talk of her willingness to do this but perhaps she was apolitical and only interested in the "art" part of it. I don't know."
I can't know why she did it. All I can say is that seeing Triumph of the Will gave me the strong impression that she believed in what she was doing. At the very least she must have understood Hitler's beliefs very well to have made it the way it was made.

"Some of the atrocities that the Nazi's later did, would have been miles above what normal people could ever imagine."

Well I certainly hope so. However, Triumph of the Will was made in 1934, after Hitler had made his beliefs quite clear in Mein Kampf. Riefenstahl can't have been ignorant of them.