Based on everything else we see on screen, he filled all positions he couldn't physically do himself with people he picked up off the street. Most of the "actors" look like they just regained the power of speech through experimental surgery, and the boom mic makes daring raids to claim scenes as part of the Gloriously Crappy Sound Man Empire.
While some cinematic experiments have been recorded in one take, Dolemite was written and produced in that take too. People arrive on screen with absolutely no idea of what they're supposed to be doing, many looking like the concept of "pretending to be someone else" is being explained off screen in sign language several seconds after the camera has started rolling. This is the only way to explain why a "Fuck you"/"No, Fuck YOU" exchange can take upwards of 20 seconds.
A scene from the trailer, featuring an apparently heavily sedated Rudy Ray Moore.