Hi Bill,
yes, the pronunciation according to the RAI dictionary is the standard one, with unvoiced s, but in neo-standard (modern) Italian the pronunciation of 's' between two vowels is almost always voiced. In fact, another important pronunciation dictionary (DiPI,
http://www.dipionline.it/dizionario/ricerca?lemma=risotto#) recommends this pronunciation for risotto: riˈzɔtto, with voiced s.