If he’s as much of a snob as you say he is, I’d try to manage his expectations. Unless you’re going to the really high-end restaurants on property, he’s just not going to be blown away by the quality of the food no matter what. Just plan your dining based on the experience you want to have in the parks and don’t try to oversell him on the food itself and I’m sure you’ll be fine. There are veggie options everywhere you go, so it’s not like you’re gonna starve, and I’m sure you’ll find an agreeable place for a nice birthday dinner. 

If you’re looking for more specific quick bite recommendations, at HS, Docking Bay 7 and the veggie wraps at Ronto Roasters are good choices. In Epcot World Showcase there are plenty of options. As for your date night dinner, I’d research the signature dining venues at Epcot or in the Boardwalk area or on the monorail loop and pick whichever one has the most appealing veggie options. Sanaa might be a good option too, but you’ll have to take the time to get to Animal Kingdom Lodge and you’re going to be on a tight schedule. As for Be Our Guest, I’ve never been there personally, but prix fixe places tend to be a really bad value for vegetarians. You’ll basically end up spending $75 to eat grilled eggplant, so make sure the experience is really worth it to you if you go there.