I was thinking about your comment. I think a lot of professionals can drink/smoke and still get through without anyone knowing. Tasks like acting while stoned? I think they'll cinch it, unless it made them like sleepy or they have a bad trip.
Then I thought about more improv like shows, and One of my favorite live shows was a live taping of Doug Loves Movies with Doug Benson and crew getting stoned on a podcast. After a few of them, it kinda became tame.
Thinking about it some more - I dunno if there can be good, consistent entertainment where a crowd of people get stoned and watch the chaos. It'll probably be a fun one off at best.
it's more about being liable. The theatre is essentially a construction site with a lot of blind drops, even if the weed didn't actually impair you, would you be liable if an accident (that potentially could've happened anyway) occurs while you were high?