According to the NW 7.4 Release Notes, this is not completely true - VSS is not supported for 2003 x64 which of course also applies to the SYSTEM save sets. This is true since NW 7.3:
To prevent backup errors from occurring, VSS should be disabled for NetWorker client computers running Windows Server 2003 x64. With VSS disabled, the file system and the system components are backed up by using the legacy method, which means that the backup is performed without taking a snapshot.
For more details, please read the Release Notes.