I have no knowledge of bulemia's effect on the tonsils--but I get hard yellow-white bits in my tonsils sometimes and i've never been bulemic (and I don't get sick naturally much either).
The ones that I get are called tonsilliths (tonsil stones). They are made up of food particles, mucus, just whatever gets in those crevices by your tonsils.
Still, dunno if that's the same thing. Just might put your mind at ease if it was something as simple as tonsilliths. (listerine probably helps those, too.)