According to a team press release, the Pirates have signed left-hander Cory Luebke to a minor league contract. In addition, Tim Brown of Yahoo Sports tweets that the Pirates have also signed lefty Eric O'Flaherty. Both have been invited to major league training camp.
Luebke had an impressive 2011 season with San Diego, his first full season in the majors, making 17 starts and 46 appearances overall. He posted a 3.29 ERA and an even better 3.02 xFIP, with a 9.9 K/9. He got off to a good start the following year, but lasted only five games and ended up having Tommy John surgery. That cost him all of 2013 and he had to have a second TJ surgery, which cost him all of 2014. He finally returned in 2015, but got into only seven games in June. He missed the rest of the season after having surgery to remove loose bodies near a nerve in his forearm. The Padres had signed him to a four-year contract with two option years after his big 2011 season, but declined to exercise their first option last fall. Luebke opted for free agency. The Pirates actually drafted Luebke in the 18th round way back in 2004, but he didn't sign until San Diego took him in the first round in 2007.
O'Flaherty was a top setup man for the Braves from 2009-2012, posting ERAs of 3.04, 2.45, 0.98 and 1.73 in those four seasons, although his xFIP was typically a good deal higher. He didn't strike out huge numbers, but was an extreme groundball pitcher, with a GB% between 55% and 60% each year. He had his own Tommy John surgery in 2013, missing the bulk of that season and half of 2014. He got good results in 2014 in 21 games for Oakland, with which he'd signed as a free agent. He had a miserable 2015, though, posting a 5.91 ERA in 25 games with the A's and 13.50 in 16 games after a trade to the Mets. He lost about one and a half mph in velocity from his heyday, so that may have been part of it.
The Pirates have only one lefty, Tony Watson, who's a lock for the bullpen. Other potential candidates for a major league bullpen job are Kyle Lobstein and the mysterious Robert Zarate, although Lobstein profiles much better as starting depth. It's far from a given that the Bucs will add another lefty reliever, as they've never been much interested in LOOGYs, especially not since Clint Hurdle became manager. If they thought six of their seven best relievers were right-handed, it's quite likely they'd go with those six.