UPDATED: No he hasn't.
As they describe him, "Ronan comes from the planet Hala in the Kree Empire, and he is the Kree equivalent as the badass-inest juror and military governor in space."
Nobody had denied that Reilly was cast but, like most other actors involved with the film so far, his actual character name had been kept under wraps. Ronan was one of the names bandied about from the get-go, however.
In some versions of his backstory, Ronan is Thanos's son--which would put him at odds particularly with Gamora and Drax in the Guardians of the Galaxy. Thanos, obviously, has already appeared in Marvel's The Avengers and is expected to reappear in both Guardians of the Galaxy and Avengers 2.