Wow. I'm floored. I'm very lucky to have never encountered this sort of thing in my professional life, though it may as well have been describing my marriage.
I think what is most terrifying is that, there's nothing, as the stage manager of that company, that you could do. It specifically mentioned that they hired young, inexperienced, and powerless stage managers. And even if one of them could get their heads out of the abuser-induced slow-growing fog, and manage to say something, or take any sort of action, the stage manager in question would be discredited by the rest of the company, like what happened to Benson, in the article. No change would happen, and they'd be out of a job (though that may be better for them!) The Not In Our House initiative is the absolute best thing that could have happened, here.
It's so hard when working with strong personalities and temperamental artists (meant in no disparaging way!) to find and draw that hard line between an abusive environment and "just difficult to work with." And abusers COUNT on that. They know EXACTLY how far to push things, incrementally farther, each time. They create complicity. They cloud issues.
I sincerely hope that no one here ends up in a situation like that, because it's one in which you have no power to DO anything, THERE. The cards are too far stacked against you. Believe me.
Listen to your instincts. Hold tight to your courage, sense of worth, and boundaries for acceptable behavior. Advocate for those weaker than you. Find your resources. Be willing to cut and run. Speak fearlessly about what has happened to those outside the situation. In the sort of institutionalized circumstances described, that's all you can do.
There are, of course, LOTS of potential courses of action in less extreme circumstances, and lots within our power. But the situation described in the article is literally insane.