Jonathan Harris was on Star Trek? I don't remember that. When was he on?
I know the IMDb isn't perfect, but I can't find a mention of Harris being on any iteration of Trek,
for that matter.
Peter Mark Richman (Ralph Offenhouse from TNG: "The Neutral Zone") was on Dallas
in Season 2's "Old Acquaintance," playing Maynard Anderson, who has to dump Jenna Wade as a mistress when he gets appointed to a high-profile government job in Washington.