All signs point to Vulcans being vegetarian rather than vegan.
Tuvok was getting ready to eat Porakan eggs in an episode of Voyager. He shows no apparent disgust at the idea, other than his usual jibes about Neelix' erratic cooking skills.
NEELIX: Ah! I'll start squeezing that second glass. Breakfast is coming right up. Porakan eggs.
NEELIX: The most flavourful eggs in the sector. Scrambled with a little dill weed, a touch of rengazo, a galactic favourite. Now, these eggs were not easy to prepare. After we picked them up on Porakas Four, I had to sterilise them in a cryostatic chamber for three days. Then each and every one had to be parboiled
TUVOK: Mister Neelix, I would prefer not to hear the life history of my breakfast.
Quark serves a platter of Jumbo Romulan Mollusks to a Vulcan lady. He seems quite knowledgeable about Vulcanian eating habits and has clearly planned the evening with great care.
QUARK: (continuing) ... starting with plomeek soup, which I know is a traditional Vulcan favorite... followed by Jumbo Romulan mollusks... you can't get those back on Vulcan anymore, can you...
DS9: The Maquis, Part I
Additionally, there are innumerable references to the Vulcans being vegetarians but never a mention of them being vegans.