never know what will happen, but the combination of steel (ferrous metal) and aluminum is not a good one, and it is even worse in a salt environment. You don't ever want to lose an iron based fastener in an aluminum boat.
My fisherman buddy just had to replace his pilothouse doors. They are marine grade aluminum on a steel boat and they literally fell apart.
If it were me, and I had the time, I would remove the SS rivets and put in aluminum ones. They should be plenty strong.I doubt you will have the kind of salty humidity that I have in my tank room, but looking down the road, it could cost you a lot more.
I would bet that the zinc fasteners will corrode to failure, and it might not take very long.