I know there has been mentions of TV shows before where a Game Show host and/or announcer appeared in an episode of a show, either as themselves, in a similar role but as a fictitious character, or in a totally different role before or during their game show stardom.
FWIW, i recently came across two instances that I don't believe were mentioned before:
• Jay Stewart appeared on Hawaii Five-0 in a Season 5 episode in 1972, entitled "Chain of Events", playing a character named Marty. He was playing an ordinary person with no game show ties.
• Peter Tomarken appeared on The Rockford Files in a two-part episode in Season 5 (1978) called "Black Mirror" as an uptight commercial director.
I also saw in IMDB that Peter first made an appearance on a 1976 episode of Medical Center and later in a 1979 episode of 240-Robert.
Those last 2 shows I have not seen on TV before, but I recently saw Jay and Peter on the Hawaii and Rockford episodes on Hulu and Pluto, respectively.