You point the finger at the school for shirking "their" responsibility. Then when your child dips into hypoglycemia or a diabetic coma you will point the finger at them again for being responsible when somebody pushes the wrong buttons. Diabetes can be a life threatening disease. If my child was diagnosed with this, I would never put my trust in school personnel unless they were trained in managing diabetes. And then they'd have to prove it to me. There's too much at stake. You never mentioned whether you make the child's lunch, which I'm hoping you do so you have more control over his intake. Some insulin pumps can be programed for certain units at different times of the day. This would seem to be ideal but of course you don't know just how much of that lunch he will actually eat. And what happens on the day when he's feeling a little under the weather for whatever reason (cold, virus, etc.) All bets are off. And even if you got a phone call, would you really know what to do to instruct someone else unless you saw him yourself and assessed the situation?
I can relate how he's thriving in that environment but it seems like when you found out that a nurse would not be on staff to manage his pump, you would have made arrangements by hiring a private duty nurse who becomes consistent with your son and his condition. You have consistency, as does your son, the school is happy, its a win-win situation for all involved. You can't ask teachers or administrators who are responsible for many other children simultaneously, to manage your son's medical condition. It's an accident waiting to happen. When your son is old enough, he will be taught how to manage his own disease no matter where he is. So my suggestion above is only a temporary solution until that time comes. My daughter is hearing impaired and she became independent in managing her hearing aides, batteries, etc. when she was 7. I wish you the best of luck.