No, they can only pick up at the airport if someone calls. That's why you *do* have to pay the tolls on an inbound airport ride from Green, because non-Boston cabs are required to return empty (and thus would have to pay the tolls out of pocket).

That's not to say that on one's ever dropped off at the airport and managed to steal a fare from the upper deck, but it almost never happens and you take a huge risk doing it.