This could potentially solve the problem of money being confiscated, but the card room itself would still get raided. If the Vice sting was thourough enough they would figure the whole operation out and get the cashier location as well as the room.

The Japanese government is well aware of how the pachinko parlors operate and have chosen to ignore it. Pachinko is theoretically legal in Japan but changing the laws would be too difficult or open too many issues so they just allow the current system to operate. When I was there we got lost going to the little window where they buy back your "prizes" and a police officer gave us directions.