As Xojo requires a Database Server license for the built in plugin classes to connect to a database server.
Other plugins using the Database API from Xojo also need this license.
So with our plugin and the SQLDatabaseMBS class you need the license for Database Servers.
But if you use SQLConnectionMBS class to connect and work on the database, you are not using the database API.
So in this case you should not need a Database Server license.
Database Server license required:
SQLDatabaseMBS → yes
SQLConnectionMBS → no
This is of course only the status for Xojo in version 2013r1 and Xojo, Inc could change the rules at any time.