Bard has the potential to be a top starter. That should be the priority. A top starter is more valuable than any bullpen guy.
They can find out pretty quickly in Spring Training if Bard can be a good starter. They can always put him back in the BP.
Traditionally, pitchers have gone from the minor leagues to the bullpen in the majors--and then to the starting rotation. Nowadays, there is a sharper distinction due to increased emphasis of closers and the bullpen--and reduced innings for starters. That pendulum may swing back, however, as starters get more expensive and teams reduce the value of closers. It's time teams valued their starters again in terms of $$/innings pitched as well as the other stats. That, by the way, increases Jackson's value as a FA, and reduces Oswalt's. I'm sure Boras has made that point for Jackson.