George Raving Looney Clooney is the nephew of Rosemary Clooney.
Did you see that episode of ER where Rosemary Clooney guest starred as a woman with dementia (IRCC)...opposite her nephew Jorge? Great episode from the early years of ER (circa 1994).
...and I'll bet you there are many more than we know.
Apparently, it's hard to get into the union...kind of a catch-22. You have to have already acted to get a card, but you can't act until you get a card..?