Even using stainless steel bolts on aluminum cylinder heads and intakes, there is a concern about corrosion. In addition, those through hull photos showing the fasterner bedded with silicone, look like a leak waiting to happen. By all means, those should have a big stainless steel fender washer and a nut on the inside, don't rely on screws, because if and when that swim platform gets tapped by the dock or someting else, it could pull those out and you might not know, letting your boat fill up with water while you're away for a week or two.
As for the aluminum and corrosion, bonding may help, I'll leave that to you guys in the salt water as you have the experience and I don't, being on the inland river and lake system, I just don't have ANY first hand experience with it. Perhaps there is a coating that can and should be applied to the aluminum, to give it longer life in the salt water. After all, there are some aluminum Roamers out there
One last thing about aluminum, it comes in many grades. Cheap lawn furniture starts to corrode first week you leave it outside. 5052 commonly used for architectural and some marine work, is quite resistant to the marine environment, so it all depends on what KIND of alumnium you have.