I vaguely recall there was a kerfuffle with another artist who started as a hardcore fan of his, then began drawing, and maybe sometimes tracing, Fossil's art. I can't recall the guy's handle offhand, but the guy vehemently defended himself as not copying Fossil. I remember he had an odd habit of putting dates from the 80s or 90s on his art, and claiming he did so because it was "in a vintage style." I think some may have had a belief that he was trying to appear as though he'd been drawing in that style for years, and that if anyone was copying, it was Fossil himself, though I don't think that was ever figured out. I do remember him stopping the past-dating, and claiming to be changing his style, but not really doing so.
Similar thing put LoupGarou off art, I think. Another guy imitated him, and tried to claim he was the first. Same with Ferris, who got copied by "Dennis Pawers."