Do you mean being able to charge with your resort ID or actually putting money on your resort ID?
If you are using your card to charge, all the Disney owned restaurants and stores take this. The popcorn, ice cream, etc. vendors do not.
I have never put money on my resort ID, but I would guess that it works the same way.
No, you do not need ID. You will sign the back of your resort ID just as you would sign a credit card. If you lose the card, they will cancel it and give you another. I don't know what happens if someone else has used it though...
All your charges will come on your final bill. You can either pay the bill with the credit card that you used to get the resort ID, or pay by some other form.