I've read a couple of questions here regarding uses for spent grain, but I'm curious if anyone has ever used it in a meat smoker.
Since (most) smokers don't actually burn the "smoking fuel" directly, you should find that a lot of smoke is generated, you should also find that since the spent grain is fairly damp, the amount of smoke you obtain is larger than that from the normal smoke chips when soaked in water.
Most smokers that I've seen use a propane burner to heat a smoke box that contains damp smoking chips.
There's also a larger surface area of the grains that can produce smoke, so there you may find that the amount of grain required to smoke could be less slightly, but since you'll most likely have several lbs of it before it's soaked, you shouldn't have much of an issue with using it.
There are also comments around various forums that indicate that people use smokers to dry out their grain for using them in other recipes.
I would suggest that you try with something cheap and fairly simple (say, plain chicken wings) to begin with, and see if it works.