I believe that Charles Widmore will be on the dark/ MM side of the war.
Most of what i base this theory on is his quote to Locke "There is a war coming, and you need to get back to the island so you can be on the right side (or the side that wins)" something like that.
I believe Widmore knew about MM's scheme to destroy Jacob and we know he has a great resentment to the island, Ben, and maybe the others because he felt betrayed.
Therefore i believe MM possibly approached him and asked for his help in sending Locke his way.
It seems Widmore and MM both are most definitely in the dark side.
Thoughts?