Coming from a country which produces a lot of rice, I would treat with caution using rice hulls which are not washed. Rice is a cereal crop which cops its fair share of fungicide and pesticide throughout it's growth. Not exactly sure if it also gets a dose of weed killer to kill it and stop its growth as it becomes ripe for harvesting. It is the hulls where the chemicals sit, using rice hulls for fodder by law it must be washed, before processing.
Would only take a few minutes to put the hulls in a colander and give them a good rinse.