If you're endorsed by Gibson or whatever brands, you're not allowed to play guitars of rival brands in public. More so for PRS if you're endorsed by Gibson.
But if you're a superstar and guitar hero like Slash, you can play with whatever you want, and even big companies like Gibson can't do no shit about it!
Maybe after watching this video, Gibson's CEO and his marketing people might be feeling rather....pissed off!
Actually looks more like he came on as a guest and just used whatever equipment alter bridge had on hand. Seriously don't expect him to start using prs guitars for his concerts anytime soon.