Assuming we are talking about the code being ASME Sec VIII, Div 1, from my experience, I have seen dedicated open paths counted as the overpressure protection device and in that sense, seems it would meet the intent of the code.
However, you should treat your dedicated open path the same way as any other relief device (i.e. PSV, rupture disc) and provide all the necessary documentation of cases considered and calculations showing it is adequate.
Also, both ASME Sec VIII App M and API RP-520 Part II have discussions about accepting isolation or stop valves between a vessel and relief device.
There are those who think locking is more secure than just providing a car seal. In either case, I think it will also be necessary to establish a program or procedure that specifically addresses your car seal or lock and train your operators accordingly. Just car sealing or locking without establishing a procedure and training runs the risk of losing the open path.
