I wonder if it would matter what particle size saw dust you're talking about. I agree with Mountaineer in that fine sawdust probably wouldn't work terribly well in a pellet stove. Coarser particles might have a chance, though. With a free stove you're not out much to try.
The down draft blower boiler you're talking about is likely purpose built for fine sawdust is why it works so well. The dust is probably introduced into the airflow as it enters the combustion chamber-almost like gas in a gasoline engine. The dust is fine enough that it doesn't need a ton of dwell time in the chamber to combust completely. A pellet stove, on the other hand, isn't that far removed from a normal woodstove in that you're introducing solid particles that have to sit there and combust with air flowing around them. If the particles aren't heavy enough to stay put in the burn pot, they won't have a chance to combust.