Legally in the Boston area nothing with a motor is supposed to go on bike paths. It was a law put in place in the 80s to prevent people on mopeds from using bike paths. The end result is rarely enforced from my own experience and from what I've heard from the local electric skateboard group there.
I don't know about Boston in particular, but in a lot of places these laws only apply to class 2 ebikes (ones with a throttle). Pedal assist often doesn't count, even though it's got a motor too.