I've noticed he turns up in a lot of Sea Hunt episodes. Just about every TOS actor was working pretty steady in tv before Trek came along. And both Shatner and Nimoy paid a visit to The Twilight Zone and The Outer Limits.
Stumbled across this photo, and it made me smile. Too bad he wasn't actually on the Muppet Show!
JEDIT: He did a cameo on Muppets Tonight! in the 90's though.