I bought my boat secondhand, it already had antifoul on the legs, can't tell if there was a layer of primer between the antifoul and paint the drives come with. The bottom half on one of the legs however was replaced about 2 years ago (skeg damage due to rope entanglement). The guys at Ropewalk lightly abraded the new part and applied Trilux, there had been no problem with adhesion of the antifoul since. That's background, to answer your question, the antifoul is not being applied to bare metal where primer must be applied it is being applied to a tough paint finish. So what we are dealing with is a question of bonding. In my view if a good bond can be achieved without a primer no need to use one. The guys at Ropewalk didn't think it was needed to get a good bond, I went along with that, so far that's proven out to be fine. So in my view I don't think there is any harm in applying a primer but I'm not convinced it is actually needed to get a good bond. Lightly abrading is unfortunately needed to get a good bond, I say unfortunately because I don't like damaging in any way the quality paint job the legs come with even if just the top of it's top coat.