If they are listed on the menu under beverages, you should be able to get it as your drink. I know we did get one a smoothie as our drink at TL's Snack Shack. Ask the cashier, they can tell you for sure. If not available as a drink, you can definitely get using a SC. Check out my snacks thread, link below.
Last summer I was able to get a frozen Coke as my drink at Liberty Inn in Epcot. At resort CS locations that have milkshakes and/or slushies it's been a long time since I've been able to get these frozen drinks as my meal drink but as desserts and snacks are still an option. Though, at AoA last summer the create your own smoothie was not a snack or dessert option while the other smoothies all were. That was the only one that didn't have the DDP snack symbol on the menu. If the drink is listed as a snack credit then you should be able to at least get it as your dessert but I would definitely ask the CM entering your order in the computer what options you have so there's no guessing. Different locations and even different CMs may do things differently.
