I loved Rambling Jack and went to see him whenever he came to town, if I was aware of it, and he always sang some Dylan songs but I never heard Dylan sing a Rambling Jack song. Jack was not in the same universe as an artist as Dylan and he'd be the first to admit it.
I'll probably go see this movie but I've read Wald's book and heard the "goes electric" story so many times that I just wonder what they could add to it. Maybe I'll be surprised.