Butler is a 6-4, 260 lbs tight end who was part of the 2009 NFL Draft class (undrafted). He bounced around the league on numerous practice squads as a rookie. Butler spent the 2010 NFL season with the New England Patriots on the practice squad and was with the Patriots through camp.
Butler has 4.5 40 yard dash speed and will most likely provide insurance if Rob Gronkowski is unable to play the Super Bowl. Gronkowski is suffering from an ankle injury and was noted that he wouldn't have practiced if the team had met earlier this week. Dickerson, the TE placed on the IR, missed practice prior to the Ravens game so the injury isn't too much of a surprise.
Dickerson seems to be a long term project by the Patriots, so placing him on the IR protects him for the season. Also, even if Dickerson could play, he's an entirely different player than Gronkowski. Butler will provide a much closer player to Gronkowski in case of a worst case scenario.