No Ivy athletes are coming to mind as making cameos on shows. But Gilligan's Island had quite a few Los Angeles-based athletes making appearances. Some I knew, some I caught recently with my kids.
In addition to LaRusso (Lakers), there was Roman Gabriel (Rams), Walt Hazzard (Lakers/UCLA), Jim Lefebvre, and Al Ferrara (both Dodgers
And I tell you- the episodes still hold up well!! Highly recommended!
All that said, there are several Ivy athletes who had successful acting careers. Among others, the late Brian Dennehy, Tommy Lee Jones, Andrew Shue and I'm sure others that I'm not recalling...