Veggie is a good guide but remember no alcohol too (or vanilla as I learn from that link, didn't realise that!!!), missed that bit out, sorry!
As long as there are options available, unless anyone is being particularly picky I can't see a problem, if I was veggie/vegan I wouldn't make a big fuss over dietary requirements if it were me, with it being a buffet I'd just pick from what I could eat, especially with it being a wedding, it's not like they are paying for a meal.