Android SQLite with ContentProvider and BaaS

Can BaaS solutions such as Firebase and Parse be used with an already existing SQLite database locally, and interfaced via a ContentProvider that was already configured?

I could only find information so far on using each solution's proprietary local storage solution. However, if I just treat the BaaS as a REST API, is that a feasible solution?

I'm interested in using a BaaS at this time for my first app for data synchronization/user authentication across devices, and eventually learning how to set up my own server for projects thereafter.

Thanks!