Rice isn't inert like sand and would be a breeding ground for hordes of bacteria with the least bit of moisture or contact with feces. Your reptiles would be sitting in a bed of bacterial bloom all the time. My two cents.
Even without the bacteria possibility, unless you feed your snake outside of its enclosure, ingesting rice would be a problem. Aspen, Repti-bark, and other commercially available substrates are inexpensive and safe. It is probably best to use them.