David Meeker's Jazz on Film site lists:
Lorenzo Tucker, The Pope Sisters, Bobby Hargreaves Orchestra, The Six Sizzlers, Harlem’s Apache Chorus.
I'll ask Mark Cantor if he knows any other musicians in the film.
Mark responded:
The Bobby Hargreaves orchestra is indeed a very obscure unit. Your film scholar associate is probably aware that there are two bands in Underworld....the Hargreaves band and the one led by Billy Hick, both with different personnels. At or around the time this film was made Bobby Hargreaves and his Orchestra was featured at the kit-Kat Club in New York City. In terms of the tenor saxophonist, I think that this may well be Sonny Fredericks, Jr. Frederick recorded around this time with both Red Allen and Buddy Johnson, and he solos on a half-dozen tracks, perhaps a few more. I have never made the time to compare his sound on the recordings to the tenor sax on soundtrack, and therefore (possibly) confirm his presence. If your researcher carries through on this, I would certainly like to hear back from him/her.