I have a Quantum SDLT 320 drive in a Dell 2800 server that has the yellow attention light stuck on. It is performing backups successfully in Veritas and giving no errors from Veritas or anywhere else. Can the drive be "reset" to turn off this light, and how do I do it? The computer has been turned off/rebooted since the light became stuck on, but it refuses to go off.

Sounds like it may be the cleaning light (far right)

You need to use a cleaning tape in the drive (they do expire after either 20 or 40 uses so use a brand new one to be sure)

That should clear the light. If it comes back on after another backup then try using the cleaning tape again and then a brand new tape for the backup.
If the light comes on again then the drive will need to go for repair as the head is knackered.

Try www.tape-drive-repair.com for this as they are pretty good price wise and also offer a 1 years warranty on their drives and repairs

Thats the cleaning light insert the cleaning tape and let it do its thing.Once this is done you should be fine