I bought some yeast and guess what it says on it? (I'm throwing it out).
Ingriedients: Yeast, Sorbitan Monostearate
That's not vegan.
http://en.wikipedia.org/wiki/Sorbitan_monostearate the stearate comes from tallow.
This is Hodgson mills yeast, beware all fellow vegans.
I just looked at Red Stars website and it says all their yeast products are vegan. http://www.redstaryeast.com/products/red-star%C2%AE
I don't know about Hodgson Mill, though.
Edit: Hodgson Mill says their yeast is vegan, too.