Hanrahan is a solid reliever, nothing more.
Still, not quite sure I understand the purpose of the trade, other than it being a pure salary dump. They're collecting AAAA 1B/OF types in the hopes that one will break out? Not sure that's the best strategy. I think Pimentel's ceiling at this point is that of Hanrahan, I don't think he's going to make it as a starter.
The other two guys, I would assume won't be difference makers (not that I'd expect one for Hanrahan). If Melancon is one, he's a decent pitcher (don't look at his ERA) but you can find 10 Melancon's on the open market, the Pirates have found pitchers just as good if not better without giving up any player assets in the recent past.