No, the Muppeteers didn't do the voices in the Fraggle cartoon. They were done by these voice artists.
TOWNSEND COLEMAN: Gobo, Architect, Wrench
BOB BERGEN: Wembley
BARBARA GOODSON: Red, Wingnut
MONA MARSHALL: Mokey, Cotterpin
ROB PAULSEN: Boober, Sprocket, Marjory
PAT PINNEY: Uncle Matt, Pa Gorg, Flange
PATTI PARRIS: Ma Gorg
MICHAEL LASKIN: Junior Gorg
JOHN STEPHENSON: Doc, Philo, Gunge
STU ROSEN: Storyteller