If you do not do online check in and have a room only reservation, you should be able to use the gift card to check in. Some have said that they were able to get the money returned to their credit card and then use the card for payment. I know that they have tended to charge my balance early the morning of check in.
I know that once, I called and paid all but about $50 of my balance with my gift card a couple days before my check in day. That way, only a small amount was left that went to my credit card that morning of check in.