Camping is allowed; campers do not need to leave at park close of 10pm; that applies to day use only.
They only allow camping in the camping areas, and climbing to the top in the dark can be very dangerous. If you're wanting to do milky way photography you might get a better composition shooting in the open field north of the dome since the milky way core is to the south this time of year.
Thanks! Your answer is awaiting moderation.