There may be no Symantec drives for this device, but if NTBackup can see and use it with the mfg drivers, BackupExec should be able to also
The only thing the HCL means is that the device has been tested with that particular release
(You are aware that v9.1 went End-of-Life back in January, right? I agree that if everything still works, there's no good reason to upgrade, but if you ever do have problems, you are on your own)