I presume you are using aluminium anodes because you are in brackish water
The Pettit Barnacle Barrier uses zinc. if exposed to freshwater zinc develops a layer that prevents it corroding an acting as an effective anode (hence it is not recommended for brackish water). I would expect that this would also reduce the effectiveness of the antifouling.
Most of the marine
paint companies have some technical advice facility. I would certainly ask Pettit if Barnacle Barrier will work
in brackish water
I cannot see any reasons to worry about galvanic activity (but ask). The zinc and therefore the Pettit Barnacle Barrier will corrode in preference to the aluminium anode, or a the saildrive
itself, which is what you want.
None of the prop based antifouling paints work fantastically well so do not expect wonderful performance even if it is deemed suitable.