The rule regarding who does and doesnt tent is as follows:
Thru hikers (starting and ending 50+ miles outside the park) are required to give up space in the shelter for a person with a reservation. They hold 4 spots open for thru hikers during season. The assumption is that if you are not a thru hiker, then you are one of those that has a reservation, therefore you dont need to be tenting. A thru hiker must ALWAYS give up space in the shelter for a non thru hiker with a reservation. If you dont, and the person relays that information to a ranger (and the ranger finds you), you could be fined.
Many of the folks that get reservations at the shelters are not actually carrying a tent. That could be another way for your group to cut down pack weight.