Yes, you can use your Disney Gift Cards to pay for purchases at the two Starbucks inside the parks (I've done this). You can also use your Starbucks gift card, if you have one, at those locations (I've done this too). I also think that you can use the Disney Gift cards at the QS/TS locations inside the parks (I haven't tried at a TS location, but I haven't had any issues at the QS locations where I've tried using a gift card). There are a few "cash only" snack vendors that do not accept gift cards (mostly the ones that walk around or when the card reader system is down). Note that the Disney Gift Card is not accepted at the third party locations within DTD.
