As the PPs have said, you can use Starbucks Gift Cards, including the the app, to purchase items at the two in park Starbucks locations (if you have an AP, you can also get your AP discount). You'll earn points/stars, but you cannot redeem rewards. Also, they usually do not participate in any of the special offers/discounts/promotions being offered at the regular Starbucks locations. You can redeem rewards at the Starbucks locations in DTD. I've used the Starbucks app (my gift cards were linked to the app) many times and haven't had any problems.