It says it closes at 9:00pm, is there a gate that blocks it off or is open for a sunset hike?

There's no gate. I was there well past 10 PM.

It is open

I've been up there at all hours and it's always open. I do know that the gate to the Hope Campground closes at around that time, but you don't need to worry about that if you're hitting Buffalo Peak or any of the other camping spots.

It's open.