I don't think the drawn figure of a waiter in the background of this spectacular dance sequence is supposed to be Paul Whiteman. The sequence is from the film's final ballet, in which Gene Kelly worked out a series of dance sequences inspired by late 19th century French artists. This particular sequence is based on the works of Toulouse-Lautrec, with Kelly as the Black dancer "Du Chocolat," one of the cabaret entertainers for whom Toulouse-Lautrec did posters. Another one was Aristide Bruant, and I think the heavy-set waiter figure in the drawn background is supposed to be Bruant.
Incidentally, about a year and a half ago the San Diego Museum of Art did an exhibit on music and musicians as they had been depicted by artists over the years. The Museum has a large Toulouse-Lautrec poster collection and one of the most startling pieces in their exhibition was a painting on ceramic of the French singer Yvette Guilbert. I was astonished because I hadn't realized any of the entertainers painted by Toulouse-Lautrec, who had died in 1900, had ever recorded -- but Guilbert did, and I was moved by the exhibit to order online a copy of a 10" LP reissue of Guilbert's records from the 1930's (she lived until 1944) that not surprisingly used Toulouse-Lautrec's image of her as the cover.