Please keep in mind that auto-populating your CMDB using a discovery tool will lead to an out of control configuration management process.

What we do is the following: we get the inventory from OCS, export it to CSV, and then import it to OTRS using the ImportExport feature. That way you'll have an starting point for your CMDB and any change you perform after that should be done by hand either through the change process or the configuration process. I know it sounds too manual but that way you'll keep control on the changes performed to your configuration items.