Just to add, the resort lots are small. They are designed to accommodate that resort's guests and those with ADRs in about a 3 hour window around the ADR. The lots simply couldn't accommodate all the people who would park there and go to a theme park. The resort's guests wouldn't be able to find parking spots if theme park parking was allowed. And, well, what other options do the resort's own guests have. Really none. Just saying all this so people understand why there have to be restrictions.
So, absolutely, at your ADR time park there and enjoy it but not too long before or after.