I think Cameron has a political obsession with this broad tradition. In addition, as a well-rounded film maker, he doubtlessly has deep knowledge of Riefenstahl's work.
Maybe I miss the point, but I think it's saying too much to specifically say that Cameron is obsessed with Riefenstahl. They have some things in common. That doesn't mean he's obsessed with her.
Don’t worry - I know the argument is a hard sell, but I believe the connections are deep.