I think it sounds cute. When my ex and I were still engaged, we were going to have a wedding in World of Warcraft (since we played it together) sometime after we would have gotten married. I've been to someone else's in the game and it was fun. I know that's a whole different game, but I think being able to spend time with a significant other or doing silly little things like a wedding or such still can be precious and memorable.
It'd just be roleplaying. Just pick a bunch of furniture, set it up in a room, and then invite a few people over to attend or to be giving the two players' vows.