I just went to several sources for the recomended procedures for checking shore ties and they all concur that you must turn off the power at the shore post and the breakers in the boat before you plug in the cable. Then you turn on the shore power, verify the polarity indicators in the boat read OK then turn on the boat breakers.
You could not use a shunt trip for the post and follow this procedure without taking a long walk to a location you may not be aware of. That would encourage people to handle a hot cable in a wet environment. Bad idea.