Daycare won't allow pull ups during naps

I am writing because there was a miscommunication regarding potty training with our daycare.  We kept our son (age two and a half) home Wednesday last week so that we would have 5 days to potty train him.  His teachers knew about this, confirmed that they thought he was ready, and wished us good luck.  We all worked very hard, and our son is now potty trained.  However, he needs a diaper while he sleeps.  The class we used to potty train (as well as book we read to prepare), let us know that small children often need diapers to sleep when they are starting potty training.  When we arrived at daycare today, we were informed that there is a lot of paperwork we should have done for potty training as well as a meeting we should have had with his teachers in advance.  They say they will not put him in a diaper while he sleeps.  This is very frustrating as we had no idea any of this was necessary or that they would not use diapers while he sleeps.  Our son has worked so hard, but he cannot hold it while he sleeps.  It feels incredibly unfair to refuse him diapers while he sleeps.  We can work on removing diapers during naps, but it feel unnecessary and overwhelming.  Does anyone else have experience with this?  The research I read says there is no harm in using diapers or pull ups during naps early on.