Although he receives no additional billing for it, a heavily made-up Leroy also plays his own grandfather. (Those teeth are a dead giveaway.)
During part of the "Restless Feet" number, LeRoy's tapping is obviously post-dubbed, as the fake snow he's dancing on would have muffled the sound of his taps.
Vitaphone production reels #1833-1834
Needless to say, Mary Joan Martin is not THE Mary Martin (whose middle name was Virginia).
Production Code approval #0414.