What is the exact language of the grant/easement ?
Without that, any responses are merely a guess.
From what I have read, if there is no specific language stating that maintenance of the easement will be split 50/50, then there is no "default" assumption that you have to share in half the cost of maintaining the easement ... in this case, snow removal.
If you are not using the same easement for your own access(driveway), then he would truly be hard pressed to present to any judge a reason why you should share in half the cost of snow removal, when the removal is only for his benefit.
There should also be specific language as to what they can do to the easement construction-wise.
Personally I think the guy has a huge set of balls to even ask you to share in the cost of snow removal.
As Shamus said, I would simply ignore him, and if he broached the subject in person, with me, I would tell him that he has a huge set of balls and then tell him to "piss off".