I understand you get moisture from the butter and the meat but for a crock pot to work properly it requires it to be 1/2 to 2/3 full of liquid to transfer the heat. I would be concerned about the amount of time it would take it to get up to temperature and how long it would be in the "danger zone" for bacteria. Everything needs to get above 140 in 2 hours or you risk getting sick. Crock pot normally around 170 so you won't get there in time.
Recipe looks interesting and worth a try, but I'd do this one in the oven.
Thanks for the recipe.