Yes, the parking gates open about 8:30 I think, and they let you in the park around 9:15, but dont expect any shows. Also only england and scotland are open at that time, everything else doesnt open till 10:30-11:30.
If you plan to be at the toll booth at 9:00-9:15, you'll be fine. Tolls are always open by 9, England (including Forest of Fun) is always open by at least 9:30. And yeah, you can get breakfast (including beer if you're so inclined at Squire's Grille. Also, they sell Starbuck's at the candy shop. I get there around then all the time, get a Starbuck's and chill in the England deck seating area until Scotland opens (I can see when they open Scotland from my seat