Grand Theft Auto V strives for realism in its excess crime fantasy. Truth in art, and all that. One of the game's writers and producers "Lazlow" Jones, known for co-writing and sometimes voicing the series' radio stations since Grand Theft Auto III, talked to Chicago radio station WGN about achieving authenticity and using actual gang members over voice actors whenever possible.
They even have say in the dialogue itself. "They look at the lines and say, 'I wouldn't say that,' so we say, 'OK, say what you would say.' Authenticity," Lazlow explained. "There's a lot of sessions where we would just throw the script on the floor. 'This is is irrelevant, let's just work on something real.'"
Sounds good to me. Reminds me a lot of the indelible HBO series The Wire with its strives towards authenticity. A good thing to be compared to, especially for a crime drama.