William Conrad (Narrator) was Marshall Matt Dillon on Gunsmoke.
Walter Tetley (Sherman) was Leroy on The Great Gildersleeve and Julius on The Phil Harris-Alice Faye Show.
Hans Conried (Dudley Do-Right Narrator) was Professor Kropotkin on My Friend Irma.
Those are the only ones I can think of that had regular roles on a show. With a little research, I'll probably discover some guest appearances. Feel free to add on.