If you're going to go into wedding videographer professionally then you need to know what to expect. By laying down the terms before the event, the stills guy knows what to expect. He should also be aware that you, as a videographer, are just as important (if not more so) than the stills and he should conduct himself accordingly. As a stills photographer I never had a problem and, on the few occasions I've "done" a wedding, by laying the ground rules beforehand, it's avoided problems. To assume that everything will run smoothly is very naiive.

Wedding work is a "war" and not for the faint hearted, it's best to leave it alone if you're not prepared to fight your corner.