Can you run heating oil in a 05 Isuzu npr?

Yes, but heating oil is not taxed and is therefore illegal to use in an on-road vehicle. It has dye in it, and if you are ever stopped and they find dye in your tank, the fines are pretty hefty. While you might get away with it in your personal diesel vehicle, a commercial rig like an NPR might be under a bit more scrutiny.