separating art from artist is always awkward. Refuse to listen to Wagner because he was anti-semitic? Refuse to look at a Caravaggio painting because he was a murderous thug? Refuse to watch a Riefenstahl film because she was a Nazi?
In fact, Riefenstahl's films of the Olympics is imitated all the time, every time a camera glides over an athlete's body: she was pretty much the first one to do that. Was that a "Nazi" film technique, though? Quite possibly: admiration of "muscle", of power, of strength - especially the strength of individuals rather than the masses - is more a rightwing thing than leftwing.
As for Hitler: I'm with the speaker on this. If his oratorical techniques worked, as they surely did, study them and see if you can adopt them. Learning from the best in the field is always a good idea. You're not obliged to use these skills to the same ends.