I've been doing a re-watch of Hogan's Heroes lately and I'm completely surprised at how many guest actors from TOS did Hogan's Heroes too.
I'll be watching and all of a sudden, Hey! There's Eve. There's Joe Tormolen. There's Sylvia. There's Korob. There's Manager Lurry from K-7. I haven't kept count but I'd say I've probably seen about a dozen guests from TOS that did Hogan's Heroes. And Marc Daniels directed his share of Hogan's Heroes episodes.
I just find it interesting because as a kid growing up in the late 70s and early 80s I watched a lot of 60s re-runs and I've never seen so many TOS guests. In Gilligan's Island for example, I can only think of one, which is Stanley Adams (Cyrano Jones).