I'm not a big fan of the Emelianenko-Mitrione fight either, but the impression I get by how Bellator debuted Mitrione and the generous promotion of him on Bellator events is that they see him as their big heavyweight superstar (a well-spoken American with a personality), and my guess is that they set this fight up on the hopes that Mitrione defeats Emelianenko, and this turns out to be his breakout performance before handing him the belt in a gimme fight.
If that's the case, the fact that this isn't for the (vacant) heavyweight title is more indicative that they actually don't want to take the risk of Emelianenko winning it, and then bouncing to the UFC once his contract's up. Mitrione seems to be the guy they want to invest in for the long-term.
Otherwise, they should've scrapped this fight, and put Emelianenko up against another legend ala Rampage, or dangle the carrot for Ortiz or Cro Cop to come out of retirement.