Do you always need a domain model for a web service?

I am creating a web service that will be hosted in IIS using the WebApi V2 framework. The web service exposes a local service provided locally by a .dll. The interface of the local service is very simple. I am following RESTful architectural constraints, and we don't have a need to store data on a database or persist the data. The response from the local service is a string that I will simply filter and parse into a JSON object before returning it back to the client. Is this cool?