this was long before cartoons were ever thought of as ‘for kids’, the target audience of this one was roughly 20-40
betty boop cartoons featuring cab calloway singing, yes, but slang has changed so much you dont realize he was singing about opium, sugar daddies, death, weed, sex, booze, and gambling back when gambling was nearly as tabboo as sex and drugs. ‘minnie the moocher’ where cab calloway is a dancing walrus is specifically about someone who does literally everything on that list but die
most of the animation studios had their ‘thing’ to make their animation stand out, disney had fluid motion linked with quality music, warner brothers had top notch dialogue with carefully crafted facial expressions, MGM had comedic timing down to the individual frame that no live action comedian could dream of achieving, terrytoons had the budget of a ham sandwitch and a fistfull of nickels
fleischer studios however had authentic jazz and heavy toned subject matter, often crossing the line of what we think of as ‘cartoon violence’ into realistic
No but seriously, Cab Calloway was a marvelous showman with an instantly recognizable rubber man act. He WAS rotoscoped for this. The animated pre feature shorts worked like promotional music videos for a few artists. Fleischers studio was quite rowdy so they probably took whatever was available at the time.