Originally Posted by CanadaDH

Yes, you can use the gift card to pay for any rate. Even on prepaid rates or those with a partial deposit, I've been able to have the hotel refund my credit card for the prepayment upon checkout to settle the final bill by gift card (although, that might not be wise if in another currency, since you will lose on the FX spread with the charge/refund process to the credit card).

The gift card doesn't need to cover the whole bill. You can apply as much as you like to the gift card, and put the balance on whatever credit card you wish. Remember you can also use the gift card to pay for anything charged to the room, which would include everything from meals to spa to ski tickets.

No limit to the number of gift cards you can use at check out.