"Presuming Cabaret becomes an open-ended run, which it almost undoubtedly will, that turns it into a commercial engagement. Add in the fact that they've raised ticket prices for it and how is it still considered non-profit?
That's not totally true. Remember, the revival of South Pacific played at Lincoln Center theatre for a little over two years. And, that in no form or fashion changed Lincoln Center Theater's non profit status one bit.
While there are many technical meanings to what makes something a non profit, let me put it to you in the simplest way possible as it relates to theatre. Roundabout is a non profit organization. Unlike commercial theatre settings, they don't have to deal with investors. Any money made on any show that they do goes right back to Roundabout's pockets to allow them to produce more shows. They have not gone through any legal loopholes whatsoever. Furthermore, ticket prices and length of a show's run have nothing to do with what makes something non profit.
"If you try to shag my husband while I am still alive, I will shove the art of motorcycle maintenance up your rancid little Cu**. That's a good dear"
Tom Stoppard's Rock N Roll