Yes, it's supported to sync same scope with multiple databases.
For example, if you have DB1, DB2, DB3, and a Sqlce CeDB4. You can provision a scope scope1 on DB1 and get the scope description and provision that scope to DB2, DB3, and CeDB4. Now you can sync all of them.
For the documentation, look at documents at
http://msdn.microsoft.com/en-us/library/bb902853(v=SQL.105).aspx. You can take a look at the sample at
http://code.msdn.microsoft.com/sync in Database Synchronization Provider Samples section.