i.e., I typed "Zale and Rizzo" into an internet search engine, and found very little. It looks like Johnny Haymer may have been offered a regular spot on a show that ended up not doing very well. I don't know the TV business but I could see that being a regular on a new show could be seen as a better job than a bit part on an established one.
Perhaps just as interesting a question would be how Kellye and Igor lasted so long (were they in every season?).
Zale was there from Season 2 till Radar left, part one which was the 4th episode of Season 8.
Rizzo came in 6 episodes later, Season 10, in Yalu Brick Road.