You may have noticed that the only muppets in that sequence are Kermit, Rowlf, and Miss Piggy. Rowlf and Miss Piggy didn't appear togetehr in that sceen, so it would make since for Frank Oz to have performed him since he was on the set at the time.
Of course, at Tough Pigs there is an anthology about the original script, where it's said that an early draft of the script had Statler and Waldorf in that scene at one point, yet they don't appear at the resturaunt in the movie. It's possible that their scene at the resturaunt was filmed and cut (but I don't know for sure). If that's true then Richard Hunt probably performed the hands (or maybe Richard did the puppetry and Frank did the hands). If there was no Statler and Waldorf scene that got cut, then I think Steve Whitmire probably performed Rowlfs hands instead, since Steve often performed Rowlfs hands when he played the piano and also liked to perform musicians.