Though it seemed that way at first, in that last scene it looked like they "harvest" Reaper blood as well, so it seems they were just "feeding" them before, like a farmer feeds his livestock.
Seeing Lincoln with them reminded me of the above discussion regarding relative distances between areas of interest in this world, because Lincoln had headed "east" toward the coast with Octavia when he got taken by Reapers, and now he's on Mount Weather. I hope they show the Mountain Men soldiers getting around at some point in helicopters or something of that nature to help explain all that.