Hard to say, maybe they scan plates and check them but there's no checkpoint or anything. You get in line, ride on, park where they tell you to, and go upstairs. I expect it would be dead easy to get a stolen bike or car off the island, even with the original (reported stolen) license plate. It's not really the ferry operators job to check whether the vehicles are stolen. And police don't put in a lot of hours looking for a stolen bike.
