I think MIB and Widmore are working together. And something that i'm almost sure is that Eloise is with MIB. So, I say Widmore-Eloise are in MIB team. There are many signs of this in season 4 and 5 but just a few people have realized it.
Why is Eloise with MIB? She wants his son Daniel, who she killed, come back. So MIB used her in his plans. She brought back Oceanic Six to the island, she suggested to take dead Locke with Christian shoes, and in ATL she is against Desmond remembering Penny. Also she was mentioned by Christian (who we know was MIB) to real Locke before he moved the Island using the donkey wheel.
Why is Widmore with MIB? He encourajed Locke to come back to the Island. He helped Locke to find to every one of the Oceanic 6. And he said several suspects things in earlier seasons. Widmore said to Locke that "a war was going to begin in the island and if he didnt came back the wrong side was going to win". ¿Which is the wrong side? ¿Who was benefitied with Locke return to the Island? Who copied his body? Yes,MIB. And also, in last night episode. Why was not anyone of Widmore guys protecting the sub? How knew MIB that Jack was going to be inside the Sub when bomb go off? Yes,MIB knew that Widmorepeople wera going to force Jack (and the bomb) to come in the sub. Yes, you may say why is the antoSmokie fence necessary in this case. They are using it because WIdmore people dont know that Widmore is with MIB. The only hole in this theory is in ATL, why Widmore sent Desmond to take Charly with Eloise? Maybe in ATL, Widmore changed his mind and is against MIB, Eloise and ATL. ! Whatever, in island Widmore know both sides (MIB and Jacob) and he knows one side has to win and it is MIB, i think.