If he is pinning relevant pictures to themed board and simply doing it at scale, is he really abusing the site? e.g: pictures of cakes on a recipe board about desserts that link back to a cookbook and he gets 4 cents per click through...
I'm a Pinterest newbie, but do you have to be the owner of a board to pin to it? At least the boards I am following now it seems I cannot pin to them.
The contributors have to be manually added to the board though.