Policy considerations and synthetic backups
The Synthetic Backup option is available under the following conditions:
■ The policy type must be either Standard or MS-Windows.
See pages 584-5 of the Windows Admin Guide I for more info:
Symantec NetBackup(tm) 7.0 Administrator's Guide for Windows, Volume I
http://support.veritas.com/docs/340105
So FlashBackup-Windows + synthetics is out. (But an intriguing concept!)