I've never eaten at a Vegan event so I'm not sure what to expect.
I've never been vegetarian or vegan and I don't have any Vegan friends. I have some vegetarian friends but they're never evangelical about it so they're fine with me eating meat in front of them. I've eaten some vegetarian meals before, and I'm okay with that but I don't know what typically vegans eat since I don't have exposure to that crowd.
I have soy and gluten allergies although fermented soy like in tamari is okay.
I'm planning to eat Chipotle before I go.
I know a lot of Paleohackers used to be Vegan or have Vegan friends so maybe they can give some better suggestions on eating. TIA.
UPDATE: So most of the food was various concoctions of seitan (thou art my enemy) and tofu (oh no!). There were a few nuts to nibble on. I ate before and after at home!
I wouldn't fear this at all. My standard habit is to eat some meat before I go; dainty eating at the event isn't a sin and I know my eating started with my favorite food.
Then, I'd troll the event in hopes of finding some really nice fruit/veggie dishes you might not see every day. If nothing looks good, I'd be astonished if they don't offer raw fruit and veggies so you can round out the meat you ate earlier.
Let us know how it worked out!
This is impossible to answer without more details. Vegan could mean lots of fruits and veggies (most raw vegan recipes are also acceptable paleo), or it could mean that every single dish has soy and/or gluten. I agree that you should contact them in advance - it's possible that they can adapt some dishes to be edible for you if they're aware of your needs (ie. replacing soy milk with coconut or almond milk).
For the average paleo adherent I wouldn't see any reason to be particularly fearful of this event. It's highly likely there will be lots of fresh fruits and veggies. SAD events would likely be far worse for most paleo folks. However, with your allergies I would definitely contact the caterers in advance or at the very least ask them about gluten and soy-free options when you get there.
You might get "lucky" and have some sort of a tamale-pie option which may also be gluten free. It will probably have beans. If you are super lucky, you might get something fun like coconut ice cream. It will be too sweet. I would eat well beforehand and enjoy the salads.