Night shift workers at group homes, who sleep while there and wake up only to deal with problems as needed, are a similar case. The social workers doing the day shifts might object (and so might their union) if they were paid less.
MY GF is works midnight at a group home. She is NOT allowed to sleep at. She has to spend the night cleaning and taking care of the guys. There is less working with the clients(as they are mostly asleep) but she still has to clean and do mountains of paperwork. The people on midnights are assigned these chores because there is less one on one with the clients. But I assure you they are kept very busy on most nights.