To the best of my knowledge, there is no limit on how many Universal spells can be learned, for anyone. So far as I'm aware, the limits on spell access for various professions applies only to learning spells in "professional" spheres. For fighters, rogues, etc., who have no "professional sphere" access, I would assume that to be zero unless they buy some sort of sphere access as a talent.
Those who are more knowledgeable on the subject than I, please correct me if I am wrong here.