They put him right into the starting rotation, which they don't do unless they think he's a prospect.
This might be the same guy:
"It’s the first reported European signing in the new international signing period. 19-year-old Spanish right-handed pitcher Ramon Rosso has signed with the Los Angeles Dodgers organization. The player of CB Barcelona apparently impressed the scouts during the Dodgers tournament in Valencia in February and later at the MLB Academies Tournament in Sant Boi. Rosso has made eight appearances for Barcelona in the Spanish Division de Honor, starting seven games. He went 1-5 with an ERA of 5.17 with 50 strikeouts and 48 walks in 38 1/3 innings. He reportedly reaches 90 MPH with his fastball. Besides Federico Celli, Misja Harcksen, Federico Giordani and Sven Schuller he is the latest European minor leaguer in the Dodgers organization. Fellow Dodgers signee Joel Valera got released this spring."
However 7/2/15
Ramon Rosso, RHP
— Dominican Republic (b. June 9, 1996), 6-4, 215
— signed by Juan Garcia-Puig/Doug Skiles/Engle
So I don't know if they're the same guy, maybe he pitched in Spain then moved to the DR. Or there are two different guys with the same name signed by the same team in the same year?
However, no record of him pitching in the DSL until this year, maybe he had a arm injury, got cut by LA, and picked up by the Phillies.