Do people use rice to smoke heroin?

No. Dealers put heroin in bags of rice (especially in the summer) because the rice keeps moisture from getting on the bags. When bags of heroin get moisture on them the heroin "melts" and sticks to the insides of the bags and then the user needs to tear open the bag completely and use a razor blade to scrape the melted heroin off the sides of the bag instead of just being able to open the bag and dump it out.