In most stadiums they will have their own security and police enforcement. The JW can't do anything about it, it's a city ordinance or the venue's policy, since the International conventions will be held in major NFL stadiums, you can expect some of this security searches just like you would be searched when you attend major sporting events.
The attendants will not be doing the searching, their training (there's a video showing them what to do and so on) does not include any security searches and stuff.