Can he be a major-league left-handed relief specialist?

Absolutely. He hit a rough patch with the Orioles in 2011 — he allowed five home runs in 10 2/3 innings, leading to a 10.13 ERA — but even with that he has a 4.33 ERA (102 ERA+) in his major-league career. He has a 2.86 ERA in AAA. By defninition, left-handed relief specialists aren’t terribly consistent, because if they were consistent they’d move into a more significant role. He declared free agency when the Orioles tried to remove him from the 40-man roster and signed with the Diamondbacks; he signed with the Dodgers for 2012.

Could he move into a larger role?

He’s pitched well enough in AAA to suggest that he could, but he’s a sidearming lefthanded pitcher, and the conventional wisdom is that sidearming lefthanded pitchers are very vulnerable to right-handed batters. So he probably can’t move into a larger role and almost certainly won’t.