I'd think the current flow would only effect the rate of corrosion as a consequence of it's heating effect which in the case of a great lump of 316 carrying max maybe 15amps inc spots would be negligible and I'd still advocate that connecting an electron donor to the frame will help protect it. The anodes fitted to the outboard are to provide galvanic protection to aluminium because of the environment not to offset the effect of the negative ground system. MGN28 for commercial coding has you electrically bond all the metal parts of the boat in contact with the water and there is a fair chance your "A" frame is going to be in contact with the water be it through mounting bolts or a little pool off salt water where it shouldn't be. However that great lump of 316a is still going to be there long after we're gone so, connected or not, it's probably academic.
My understanding of the RF implication is that most aerials work more efficiently with a "ground plane reflector" although this is a generalisation and maybe there's a radio ham out there who could enlighten us.....Lightning?.. Open a debate about grounding masts in the sailing fraternity and it'll end in a fist fight