I was just thinking of a certain scene in the books (sadly don't have books with me, can't quote, but would appreciate if somebody did) from
Flotsam and Jetsam that may be of interest. What kind of food do Pippin and Merry offer? They don't have much - beer, bread and honey, ham. Nothing says that or dear Legolas specifically did not eat the ham, but I've always assumed everybody ate everything.
So if it makes you happy, you can debate whether Legolas was surviving on bread and honey or if his behaviour proves that Elves are not vegetarian.
I don't really feel like arguing it either way.