It certainly won't be the bullpen for the entire season. In 2010, 16 different pitchers relieved at least once during the regular season (and a 17th made a relief appearance in the playoffs). I don't really expect the 2011 bullpen to have that much turnover, but it's certainly possible.
Showing the 2010 bullpen in the same sort of roles that I've used this spring:
|Jon Rauch: Opening|
Day closer in 2010
Closer: Jon Rauch
Setup 1: Matt Guerrier
Lefty 1: Jose Mijares
Setup2/Middle relief 1: Jesse Crain
Lefty 2: Brian Duensing
MR2: Pat Neshek
Long man: Alex Burnett
By September's roster expansion, drastic changes:
Closer: Matt Capps
Lefty 1: Brian Fuentes
Setup 2/MR1: Guerrier
Lefty 2: Mijares (or maybe Randy Flores; Mijares may have been on the DL)
Long man: Jeff Manship
Four of the original seven were still there, but all in (somewhat) different roles. Crain had moved ahead of Guerrier in the pecking order; Mijares and Rauch had some physical issues; Ron Mahay had been activated, pitched much of the season and separated his shoulder; Capps, Flores and Fuentes had been imported; Duensing was in the rotation ...
Bullpen evolution can be rapid. I now project Jim Hoey, Dusty Hughes and Glen Perkins for the three "open" jobs (defined here as S2/MR1, L2 and MR2), with the likes of Manship, Scott Diamond, Kyle Waldrop and Burnett missing the cut. It's entirely possible that Waldrop, Diamond and Burnett would be better choices for their projected roles.
And if that's the case, they'll get their shots. Well, maybe not Diamond -- his Rule V status means the Twins aren't sure they'll have him in their inventory all season -- but if Hoey can't throw strikes or Perkins struggles to get outs, Waldrop and Manship and Burnett will be available.
There are a lot of candidates here I like. Burnett, as I've said, reminds of of Juan Rincon, who had a few good seasons here. Manship is comparable to Guerrier. Waldrop keeps the ball in the park. Carlos Gutierrez is a ground-ball machine. Hoey has the power.
They're all unproven. So was Nathan at one point, and Mariano Rivera, and Goose Gossage.
Unproven means nothing. Getting outs, that means everything.