Galvanic corrosion is caused when two dissimilar metals are in electrical contact with each other while immersed in an electrolyte, such as seawater. This is not likely to be an issue in your scenario. Electrolytic corrosion is an absolute possibility, however. The amount of electrical power your neighbor uses is not the determing factor though. But if he has electrical problems aboard, you could be sharing them. Or rather, you could be sharing the results of his electrical problems.
We left a "Hot" dock in Newport Beach that would destroy a prop zinc in a month. Also ruined the engine to prop shaft coupling and numerous other parts and fittings on the boat. We have an electrician on our current dock who is diligent about checking for stray current and our zincs are lasting +6mo.