Both Tim Burton and John Landis were assigned to the "Sesame Street" group (I know that because they were only about 5 feet from me-only I did'nt know it then!). I'm only sure that Landis did Grover-it's really difficult to tell exactly how did what from the photos, but he was about 8-10 characters in from the right side.
Burton was about my age at the time (18-ish) and still involved with Disney (or CalArts), so he would have not had much choice in which character he would have performed, and they would not have given him a monster or creature based on who he was, since he was still a kid just helping out on the film, like me, and hadn't become "Tim Burton" yet.