Actually, most of the time the Helo will contact the appropriate Sector on the VHF Marine CG Channels, for them to assume-their-Guard [aka monitor the radio] as well as report their position periodically. There have been a few Helo reports on the P25 channels, but limited here in New England.
They do run 164.5500 and 166.2250 for Base Ops at CG Air Sta Cape Cod
In that same band, since you are so close you will find P25 [NPS at the Charlestown Navy Yard] and Analog US Navy from the same location for the Constitution
I'll set the custom search on my PRO-96 to 162-174 while I am at home in the afternoons and see if I pick anything up. I see the C.G. helicopter flying over my appartment all the time. I assume there using a frequency between 162-174 aswell?