We dont know yet. But speculation is that it will be able to access ALL parts of your package reservation (room entry, room credit card account if any, tickets, and dining plan if any) and there will be a tap to pay option at the restaurants.
I'm not sure I'm understanding the rest of the question. You don't pay with credits when you book a restaurant. You don't pay until you are actually at the restaurant. Your credits don't even exist until you check into the resort, so there's none for the restaurant reservation system to draw from. The way it's been explained, to pay with the band you will tap it to a scanner at the restaurant itself.