The SharePoint 2010 User Profile Synchronization Service is really FIM 2010 pre-packaged in a very special way. Need evidence? Look at the tables in User Profile Service Application_SyncDB
See how it has mms_connectorspace, mms_cs_link etc. Those are table commonly found in the FIM sync database. See the attributeInternal, the BindingInternal, all of the Membership* tables those are all part of the FIM Service database. So interestingly enough they have both FIM Service and FIM sync merged into a single DB.