Before the rosters deadline, the Rays claimed Chase Whitley off waivers from the Yankees, giving him a valuable space on the 40-man roster. Whitley will be coming back from Tommy John surgery (following an injury that occurred while he was not being completely forthcoming with the Yankee's medical staff) and while there's always uncertainty surrounding rehabbing players, that status does mean that as soon as the season starts, the Rays can add him to the disabled list. The roster crunch only involves the Rule 5 draft.
And the reason why the Rays were willing to give Whitley a roster spot is that despite not having an overpowering fastball, he's actually a pretty decent pitcher.