We have a pellet stove also, it puts out a small amount of ash but no smoke when running. The issue would be, it does throw a few small embers and that would be a bedding or litter concern in your coop. It doesnt draw the same as a wood stove so from what I can tell it wouldnt be an issue to turn the pipe up or even just extend it out the other side of the coop. We put a small planter under our vent pipe to collect the small amount of ash and what ever embers it might throw because ours vents right beside the house into flower beds with wood chips. I personally wouldnt let it just vent into the coop with the chickens because of carbon dioxide and when you first fire up the stove it does smoke out the vent before the pellet tray lights completely. I just looked at your picture and absolutely you shouldnt keep it the way you have it, with the hay bale near the vent.
