It is interesting that I don't see anything particular about the grounding for a building built on a pier beyond Article 555 and that does not talk much about service equipment. Personally I would want to the the service disconnect up on the shore and a feeder with the EGC meeting the requirements of 555.15 (basically an insulated wire).
I see nothing that relieves the installer from following 250 part III when it comes to the electrode and nowhere in there does it allow a connection to the water to be a ground electrode.
In a "boat" with no shore connection, a bronze grounding plate in the hull is common.
