I am in the middle of my Season 5 rewatch (having started from the beginning this past June), and I am now convinced that both Charles Widmore and Eloise Hawking are on the same side as Jacob's Nemesis.
- Point 1- Nemesis represents fate and pre-determinism (and so does Hawking) vs. Jacob's free will and choice. Nemesis says "it always ends the same." Eloise is the foremost voice on the show regarding destiny, making sure events happen as they are "supposed to," and pushing people in the directions of their "fate."
- Point 2- Both Eloise and Widmore want Locke back on the Island after he turns the wheel. As Widmore states, "if you are not there, the wrong side will win." To me, it's no coincidence that once Locke gets there, he becomes the vessel for Nemesis. I am theorizing that both he and Eloise knew this, and were assisting Nemesis to complete his "Loophole" plan.
- 2A- It was only after Locke mentioned Eloise that Ben killed him. I believe Eloise only wanted to see Locke after he was dead, and therefore, was ready to return to the Island to be Nemesis' vessel.
- Point 3-- Both Widmore and Eloise orchestrated and ensured that Desmond got to the Island in order to push the button. This shows that despite their romantic breakup, they have always been on the same page. I'm not sure how Desmond's button pushing, non-pushing (which allowed 815 to get to the Island) and turning of the failsafe directly played into Nemesis' plan, but perhaps all of that led to Locke coming to the Island and set into motion the events that would bring him, as a both a corpse and the Leader of of the Others back to the Island to complete the "Loophole" plan.
- Point 4-- Ben has never been in contact with Jacob, and he was The Leader also. If Ben spent the better part of 2 decades as Leader of the Others, just as some combination of Hawking and and Widmore did for at least 3 decades, it's plausible that "Island leadership" has been under the influence of - if not directly working for - Jacob's Nemesis (as opposed to Jacob).
- Also, Ben was following Eloise in the Ajira 316 plans and had a direct hand in delivering a dead Locke back to the Island. It's possible he unwittingly was a servant of Nemesis for the entire series thus far.