Griffin does point out that, although the “unintegrated musicals” tended to present black performers in limited and often stereotypical roles, at least they had black performers. (And despite having an all-black cast, it’s not as if Cabin in the Sky was free from racial stereotypes.) He also suggests that the unintegrated nature of the musical numbers would in some cases have given the performers more artistic freedom. If the number didn’t need to have anything to do with the story, there would have been a better chance of black performers being allowed to do their signature number, a song by a black composer, a song or dance popular among African-Americans at the time, etc.
But on the other hand, as in the scene ElvisL1ves describes, black performers could still be very limited in these movies in that they were typically restricted to ONLY doing a musical number. They’d appear for their song and dance and then disappear at the end, often without ever interacting with any of the white characters.