MLB roster rules state that players on the 60-day DL don't count against the 40-man roster during the season, but have to be activated once the season is over. The Brewers had three such players: Chris Narveson, Mat Gamel and Alex Gonzalez. Gonzalez's pending option complicates his status a bit, but the Brewers made room for Narveson and Gamel by removing pitcher Cody Scarpetta and infielder Eric Farris from the roster yesterday.
Scarpetta was one of the top pitching prospects in the organization at one point, but he missed the entire 2012 season to undergo Tommy John surgery. He was really only on the 40-man roster in the first place because of a weird quirk with his original signing that led to his contract being voided and a new one signed.
Farris, meanwhile, was a Brewer briefly this September but his career has stalled a bit. He earned some attention by stealing 70 bases for Brevard County in 2009, but missed a big chunk of the 2010 season due to injury and has hit .277/.321/.369 in 325 games in AAA over the last three seasons. He's also almost exclusively a second baseman, a position the Brewers have filled long term with Rickie Weeks.
This hasn't been confirmed but I believe neither player will be eligible for minor league free agency. Both, however, could be selected in the Rule 5 draft.