I don't believe there's any designated areas. At least I'm not aware of any.
I recently dropped off some paxs at Patriot Place (Gillette) . After the paxs got out, and while I was parked making some notes, a woman approached me and asked if I was Uber. I responded yes. She was security and told me that Uber wasn't allowed on Patriot Place property. I left, and about a quarter of a mile away, I got a ping from Patriots Place (the movie theater). I returned from another direction, quickly picked up the paxs, and got out of there. There was no event going on.
I wouldn't pick anyone up at Patriot Place if an event is getting out. Wait on some side street about .25-.5 miles away. Most paxs realize they have to get a short distance away from the stadium for a pick up.