As long as there was nothing unusual/substituted in the food, I wouldn't mind - I would mind if, for example, there was substitutions of soya milk or margarine in places where you'd normally get dairy. I can't say I'm allergic to it, and I'm fine with small doses, but if I have too much, i get real stomach upset and unpleasant consequences. If I know that something is 'dairy free' that would normally have butter or cream, say, I can then check and avoid it if necessary. But a vegan meal might have a lot of things like that that I'm not expecting, and I'd hate to have a wedding ruined by having a really upset stomach as a result. I have a bit of a reaction to lentils, too.
However, purely vegetables that I'd be normally eating alongside a meat meal, that would be fine. It's the things that I tend not to eat normally, like anything with soya products in, or to a lesser extent, lentils, that would cause problems.
I wouldn't want to have coffee or tea or anything with alternative dairy milks, so would just skip that. Same with cake etc if it had soya butter in, as many vegan cakes do. Vegetable oil, fine.
So it really depends on the ingredients. You may find that a lot of your guests have dietary reactions to some of the food, without knowingly being sensitive or allergic to it, but just when there are more of certain ingredients than you expect, it can be difficult.
I've never had particularly nice vegan meals, but I'm not averse to the idea. I've had some nice vegetarian dishes. I've had some awful vegan meals, drinks etc., but I'm sure your caterers would be much nicer.