I love how I can post a question here and get an answer, often within the hour. Scott Reboul informs me that the four gentlemen who sung as "Creep" were Jack Brown, Bob Miller, Jim Farmer, and Keith Boone, all of whom were members of the ensemble on the TV show, Sing Along with Mitch. Scott adds, "One of these guys — I think it was Bob Miller — was one of the original Texaco Singers on Milton Berle's radio and television shows. I don't know much about Bob Warren other than that he wrote 'Haldeman, Ehrlichman, Mitchell, and Dean' and was the piano player featured on the recording." He further informs me that Creep appeared on the episode of Mike Douglas Show that featured Moe Howard and Soupy Sales and which was taped August 14, 1973.
Thank you, Scott. I knew someone would know.