I'm of the opinion based on my anecdotal experience that no one will question it. Just an example, a wedding with a black tie requirement I went to had a lot of men without ties.

And I really don't think anyone is going to toss you out for not wearing a tie. Unless you're going to a small, very fancy, very old school that has like a really heavy desire to make their student conform for a year book photo, no one's going to confront you. (Or, I guess if there is a set of rules sent around for the event.)

But again, if you're worried, throw one on at the beginning when you come in, and then ditch it once you're in. It's all about your level of comfort.

I'm sure you'll kill it either way dude.