I had a rice burning paddle fed hopper and inclined flat grate in my last coal stove. The nameplate said rice coal only.
I had a little home garden and grew some field corn. As an experiment I added corn to the rice coal. I measured by volume to 10% corn to rice and it burned just fine. Then I went to 25% and it still burned fine. I went to 40% corn to rice coal and it still burned good. I had no problem with it coking up on the grate. I was told that it wouldn't burn any corn and would instead do one of two things.
1. coke up the grate
2. burn back into the hopper and burn the house down
Neither happened or even came close. I never tried wood pellets because I figured the paddle would break them up and then I have flammable dust at the base of the hopper building up.
I would be hesitant about burning rice coal in a pellet stove due to the construction of the burn cup. Coal stoves that I have seen have heavy duty cast iron burn surfaces or refractory lined due to the intense heat generated by the coal bed. Most corn or pellet stoves have burn cups made of carbon steel. I'm no metallurgist but it would seem to me that the hotter burning rice coal would really shorten the life span of a burn cup made of carbon steel.
Now if you could fabricate a burn cup from cast iron......
New Beginning Church