If it is not on the HCL, that just means that Veritas/Symantec has not tested it, not that it doesn't work.
As long as the device driver uses industry standard calls, you should be able to load the W2K3 drivers from the manufacturer and then tell BackupExec to use existing drivers when you run the hardware wizard
Also, if you try this and it doesn't work, Veritas/Symantec will (probably) tell you to open a paid instance, and then throw their hands up and say "it's not on the HCL"
Again, it SHOULD work with mfg drivers, but if it doesn't you are on your own, with a non-useable drive (unless you also upgrade to v10, which explicitly supports that model ;) )