Yes, you may use cash, debit/credit, or a gift card.
We linked our KTTW card to our credit card at our resort in case we wanted to have tips paid for with our credit card. You can always dispute charges at the resort before checking out if you think something was charged incorrectly. We ended up using cash for part of the tips, and used our KTTW card for the rest. Linking your card is easiest since your DDP credits are shown on that card (and they already swipe that card to subtract your credits).