I can't speak to the megamods, but I have sustained no signficant damage ramming fishing boats, junks, sampans, etc. in stock 1.3 and 1.5.
Haven't tried it with a tugboat yet, but did attempt it on a severely damaged but obstinate LMT after running out of every type of ammunition. I don't recall any major damage to the boat, but there certainly wasn't any to the LMT. We just slid up onto the deck until friction took over. Even tried diving while there.
