Many countries don't have a "Megan's law". Your best bet is to call or visit the their embassy (or we-site) to find out if they have such registry.
EDIT
If that person is legally in the US then he/she is not supposed to have any sex crimes (or any kind of serious crimes) in his/her criminal record. Immigration and the U.S. Department of State is supposed to check on that before granting any visa.