In may experience, most of the time, during the "crucial" moments of a wedding, photo/videographers take the best spot to shoot from and it's very rare that a guest could interfere (the most brave do, but it's rare). In the other situations, it's usually quite easy, even for a videographer, to change frame or ask the kind guest to kindly move his back from the front of his lens, without loosing the shot. I think it's part of a photo/videographer's job to be able to do his work, leaving the most freedom to the wedding couple and their guests. Of course, if someone's behaviour is out of control, even for the most experienced photo/videographer there's nothing to do...
Much more often, I saw photographers appearing in the videographers frame and vice versa, both fighting for the best frame, both loosing the fight. That's the worst thing, in my opinion.