It doesn't specifically say so in RCI's Drink Package Information
, but since room service isn't mentioned I'd say the soda package isn't allowed when ordering room service. I do know that Carnival specifically says the soda card doesn't work for room service, and I assume RCI is the same way.
Always have some dollar bills on hand when you cruise. I'd tip room service $2 or so for each time they deliver something - more if it is a large order. Room service is usually quite prompt, but don't order something and then forget about it. I've seen too many people order breakfast on the night before, and then not get out of bed for when they requested the food to be delivered. You'll see. Lots of trays sitting outside cabin doors with all the food getting cold.