Answer:
I would advise against this. The whole point of a sous vide method of cooking is getting moist, perfectly cooked food by vacuum sealing it in a sous vide bag and then cooking it in a water bath with precisely controlled temperatures for optimal results. You just don't have that kind of control with a crock pot, I doubt you could even approximate it.
I would think you would have better results putting a vacuum packed bag of food in a saucepan of simmering or boiling water on the stove, and using a digital thermometer in the water to guide you to manually adjust the height of the stove burner.