Much safer to board smaller vessels from a rib. Less masts and antannae to get tangled in/impaled on...
Helis are fine to drop a boarding/raiding party onto the open deck of a Tanker or cargo ship..but most trawlers and smaller vessels have cranes,masts etc,which can cause major hassle for pilots and those disembarking or even winching from a heli..
I'll take my chances in a rib...at least if you fall in to the drink,there will be someone there to haul you out..