Hi mtognetti
CA is still not supporting use of REST API for clients, atleast not in current 15.3 version, I feel its mostly to avoid any conflict down the line as there CA PPM REST API are still young and subject to change with coming versions. However i have seen few clients using REST API for development and integrating other systems with risk of any future changes impacting there solution.
If you want to understand possible way to use REST API, i will suggest you to follow blogs as below:
1) CA PPM REST API
2) GEL Script consuming CA PPM REST API
Let me know if you want to know anything specific in CA PPM REST API.
Regards,
Prashank Singh