I find that the sound of the smoker gets on my nerves sometimes - last year we used ferrets a bit and i enjoyed it more without the monotonous whine of the smoker in the background all the time. the dogs can scent better too.
also, rats will bolt from one hole to another and see the dogs then will not bolt again. they will rather sit in the hole and put up with the smoke making the rat fall asleep and ultimately die in its hole if it is continuously pumped with smoke. a rat with a ferret on its tail is more inclined to bolt. smoke will not seek out rats - it finds the path of least resistance