Sounds likely. Like I say -- it happens a lot more than people realize.
In my experience, I got away with it because I was in New Orleans, and the people around me recognized what was going on. The vibe and the sound were right, and that's what people notice when they get past the meat suit and take a listen.
Still, she could have honored Otis Redding without the blackface. Some people didn't know any better back then.
Here's something interesting -- the song "Somewhere Over the Rainbow" was most likely channeled from the spirit of L. Frank Baum, author of the Oz books. It came all of a piece to songwriter Harold Arlen as he was stopped at a red light at the same spot where the Baums first entered Hollywood, and it was unlike anything else Arlen had ever written.