Removeable Storage Manager must be disabled in this case, and it is. Maddeningly, everything shows up as installed, functioning, OkeyDokey, etc. The drivers are Veritas, not Microsoft, and the installed patches both this month and last, mainly addressed security issues in IE. No drivers have been changed since last December. Which really sucks since nobody uses IE on my servers anyway so I could have avoided this by just not doing the (unnecessary) patches.
I will install the latest Veritas drivers tonight, but the docs say they address newer loaders of which mine is not one, so I think it is a wild goose chase. But I have nothing to lose at this point. Very strange that everything should report "OK" and yet still be "offline". Oh, and yes, the devices show up in device manager. (We also have a pair of standalone DLT Dell drives which are working perfectly.)