Ive seen that done as jonathan has said or if you raise the temperature of your smokehouse too fast or start too high. But for the purposes of what your wanting, after you shower them cold or place in a cold bath you can spray them with warm water or run them under a hot water faucet and it should remove any unwanted grease from the casings.
Generally any of those sausage seasonings such as hollys medium would be a great fit for venison. Typically on breakfast style sausages I add a small amount of red pepper flakes which add a nice touch for venison. Make sure to add between 20% and 30% pork fat (back fat works great). Also for your grind use the course plate and run it through twice. A small amount of water will help with meat spice mixing and grinding. Just make sure to add the water after youve mixed in the seasonings a bit so you dont get clumping.