Did you read the article in the Sunday Style section in the New York Times on vegan and vegetarian weddings? Basically the article discussed whether a couple's dietary choices should dicate the wedding menu. So for example, if the bride is vegan should the menu consist of vegan food only.
It's a tough call because on the one hand you want to stand by your convictions if your diet choice is based on conviction, versus an allergy issue.
You would assume a couple who keeps kosher or halal would serve food at their wedding thyat follows kosher/halal guidelines without any questions, but I guess since vegan and vegetarian are seen not as a religious choice but maybe an ethical one the question is whether you would "force" that choice on your wedding guests.
My opinion is that you should serve what you want to serve. Your guests will survive a night without meat if you choose not to serve it. Today most caterers can create a delicious menu that is 100% vegetarian. Vegan and gluten-free may be a bit trickier but if it's really important to you and your groom then do your homework, and make sure to put more money in the catering budget since going against the norm may add to the menu price.