If we arrive at 10pm can we still get in the park to our reserved camp spot?

Yes, campers can arrive till 10pm. Quiet hours are from 10pm to 6am and it would be good to arrive a bit early to setup.

There is a front gate where the park rangers are and they basically check you in, and you have to have a pass to be able to park in your reserved area. I do not believe it is a good idea because the park rangers will not be there.