I believe they do open the parking lot earlier then 9:00. 9 is when the park itself is scheduled to open.
However, they will usually start to let people in the park gates at 8:45, at least into the park area near the gate. This is to allow people to get breakfast at Cypress Bakery, to get park maps, and start to schedule their days. You can also go ahead and make any reservations you may want to make for the day. I can not with 100% confidence say they do this each and every day, but I really think they do.