Here's a reminder of Rick Hurst in M*A*S*H (from this thread):
And from the Trivia thread, you'll recognize "A" as Mary Jo Catlett. She arrived at the 4077 with Blythe Danner (i.e. Gwyneth Paltrow's mother), who was a central character in that episode. Unlike Blythe, Mary Jo got to make a couple more appearances (one of which was on TV last night).
Considering the overlap in production runs of Dukes and M*A*S*H, it's hardly surprising that actors turned up in both. As an example, a couple of weeks ago i spotted Teddy Wilson in M*A*S*H - he was Morgan, one of Helen Hogan's heavies in 'Route 7-11'.