While possums conceivably CAN carry rabies, it's very, very. VERY rare.
http://www.wildliferescueleague.org/report/opossum.html
and from: http://tampabaypest.com/Services/Opossum/tabid/57/Default.aspx
http://www.wildliferescueleague.org/report/opossum.html
and from: http://tampabaypest.com/Services/Opossum/tabid/57/Default.aspx
Opossums, like most other animals, are susceptible to infection by the rabies virus; however, very few rabid wild opossums have been documented. Extremely high doses of the virus have been required to experimentally infect opossums as they seem to be highly resistant to the disease. Even though they do not often carry rabies, opossums can still deliver a nasty bite.