Certainly they must walk the halls of Bethel, do occasional shopping, go to Home Depot or get out and do chores like everyone else. If you know what they look like and are respectful, they should feel no qualms about shaking hands and chatting a few moments, right? Living in a Washington, D.C., suberb, I've seen Sandra Day O'Connor, Al Gore and many other notables. I've seen actors, well known journalists and a friend of mine went in to pick up a pizza some years ago and a little old man in very casual clothes walked in and was waiting behind him in line. He nodded at the man, who nodded back politely and then recognized him as Admiral Hyman Rickover. It happens so often that I've lost count.
I respect their privacy and have never intruded, but I could have if I'd chosen to. And were I a JW, I'd feel comfortable saying hello if I ran into a GB member. (After all, I help pay his salary, right, or I would if I were a member of the Kingdom.)