Please correct me if I'm wrong, but I don't think that grounding an object will change the corrosion. Basically you have a chemical reaction between the two dissimilar metals which is creating an electrical current which is eroding one of the surfaces. Now, if both of them were grounded, you might not get the corrosion...Aluminum rivets probably pose some corrosion risk, but I wonder if the mast is grounded, then the corrosion ends up in the zincs, and all is well (zinc is below aluminum on the series).
I certainly have locations where I have corrosion between a stainless part and my aluminum toe-rail, which is well grounded. Applying an anti-corrosive coating between the surfaces, such as Tef-Gel, will greatly reduce the corrosion.
-- Geoff