I assume the Pirates will go with a 12-man pitching staff, because they usually do, even though it shouldn't be completely necessary with so many days off in April. With that in mind, here are my best guesses.
NEAR-LOCKS
SP Paul Maholm
SP Ross Ohlendorf
SP Zach Duke
SP Charlie Morton
RP Octavio Dotel
RP Joel Hanrahan
RP Brendan Donnelly
RP Evan Meek
That leaves spots for one starter and three relievers.
Unless someone like Chris Jakubauskas or Brad Lincoln swoops in with a great spring, the fifth starter job will be a competition between Daniel McCutchen and Kevin Hart. Both have options left, so the Pirates can send the loser to the minors. In a fair fight, McCutchen, who outpitched Hart last year, would win. But Hart was first in line for playing time last year, and because of his superior stuff and the fact that he's more of a groundball pitcher, the Pirates may give him the first crack at the job just to make sure, yet again, that he can't throw strikes as a starter. I wouldn't exactly cry my eyes out if that didn't happen, but I bet it will, although I think he'll be on a very short leash. So let's say Hart wins the fifth starter job. If McCutchen wins the job, I think Hart will have a good shot at a bullpen job, but if Hart wins, I think McCutchen heads back to Indianapolis.
In the bullpen, D.J. Carrasco is pretty darn close to the "near-lock" category. True, he's signed to a minor-league deal, but this is a guy who threw a ton of innings in a tough league and a tough ballpark last year, and still put up decent numbers. Of course his arm could explode at any time after throwing all those innings last year, but he's a pretty good pitcher, and he should and probably will get a spot.
That makes five pitchers in the 'pen so far, and no lefties. There is precedent for a team going with an all-righty bullpen, and actually Donnelly played in some all-righty 'pens for the Angels a few years back. I think the Pirates will be reluctant to go without a lefty, though. Donnelly, Hanrahan and Meek historically have handled lefties pretty well, but Dotel and Carrasco have not. So Javier Lopez, who is signed to a major-league deal, is pretty likely to get a spot--he and Donald Veal are the only lefty relievers on the 40-man roster, and the Pirates will probably want Veal to pitch as a starter in Indianapolis. So unless the Pirates really want to dig through the scrap heap for someone like Justin Thomas, Brian Burres, Jack Taschner or Wil Ledezma, Lopez is the guy. Neal Cotts could figure into the bullpen mix later in the season, but he won't be fully recovered from Tommy John surgery until the summer.
That leaves one spot, and the Pirates will have all kinds of options to sort through: Steven Jackson, Brian ("Don't call me Burres") Bass, Vinnie Chulk, Jeff Karstens, the loser of the Hart/McCutchen rotation battle, and others. Chulk might not be a bad choice, but my money is on Jakubauskas here--he's already on the 40-man roster (in contrast to someone like Jackson, who seemed to be a likely candidate before he was removed a few weeks back), he's capable of soaking up innings, and he didn't embarrass himself as a Mariner last season.
A dark horse for that last job, though, is Jean Machi. Machi has never been regarded as much of a prospect, but he put up nice numbers--albeit with low strikeout rates--at Altoona and Indianapolis last season, and then he was ridiculous in Venezuelan winter ball, posting a 1.95 ERA, racking up grounders, and striking out four times as many batters as he walked. No one took him in the Rule 5 draft, which might tell us something, but if he pitched well out of the gate in Spring Training, I wouldn't be at all surprised if the Pirates perked up and paid attention. Until that happens, I'm going with Jakubauskas. So here it is:
PITCHERS (12)
SP Paul Maholm
SP Ross Ohlendorf
SP Zach Duke
SP Charlie Morton
SP Kevin Hart
RP Octavio Dotel
RP Joel Hanrahan
RP Brendan Donnelly
RP Evan Meek
RP D.J. Carrasco
RP Javier Lopez
RP Chris Jakubauskas