My current stance is, if the parking lot "is closed" and it is getting close to published theme park opening time or the time of your breakfast advance dining reservation, that you should make an attempt to enter the lot anyway.
A year ago my suggestion was to let the maitre d' know that you were late because the parking lot was not open yet, and expect him to seat you pretending that you were exactly on time for your ADR, escalating the issue to Guest Relations if needed.