Oh, god, people are so twatty.
If you get invited to a Hindu wedding, the chances are the food will be vegan. And fabulous. Would people refuse to go because the food isn't meat based?
I might not choose to go to a vegan restaurant, but to be invited, by a vegan couple, to be hosted by them, at their wedding, why on earth would I expect to be served meat? Would I go to a Jewish wedding and expect to be served pork?
Do it in summer, have a marquee and a fabulous buffet: salads, veg tarte tatin, polenta and roast veg stacks, puffed pastry patties and tartlets with mushrooms, etc.
Don't use 'substitutes' that taste horrible to a non-vegan, e.g stuff made with vegan 'cheese'.
Serve some gorgeous puddings and deserts.
Be free with the drink during the meal, even if you have a pay bar after.
Hardly anyone will notice.
And so what? To be INVITED to something and then moan about what the host provides is seriously ill mannered and not in the spirit.