Interesting word, coined by an interesting author. I would assume that nulutative would derive from nulutatus a past passive participle of a putative verb nuluto (-are) of unknown origin or meaning. I don't think nullus comes into play, save that it was some kind of mistake on Brin's part, because there is but a single l in the word under discussion. Hmm, my first WAG was that it was some negative (i.e., with n(e)-) version of ululate (from Latin ululo 'to howl').

Ceci n'est pas un seing.