What kind of rice can I use in a salt shaker to prevent clumping
I do this at home, and it makes a significant difference.  I suspect that it is the mechanical action of the rice, but since adding a teaspoon of rice to each shaker, I don't have to get out the toothpick ever few weeks to clean the hole.  

Brown rice includes the germ (embryo) of the grain, which contains some oil.  This oil goes rancid, which has an unpleasant smell.  In the quantities that you are using, and that the oil is still inside the rice, I don't think you would notice.

Note that it doesn't have to be rice.  a few beans, some barley, lentils, or wheat should work just as well.