I hope you've had better luck with the DELL ML6000 than we did at my previous job. They had to come in and replace the robot mechanism more than once. I understand that the system is the same one that is rebranded by Sun and other vendors, but the selection of other components and the assembly can make a big difference.
I was in the same situation. The Windows guys pushed through the purchase and got their server designated as the backup server using Veritas NetBackup on Windows NT.
You should be able to find drivers for UNIX/Linux (either from DELL or from another company that sells a comparable library with the same basic components). Get it working with mt to handle the tape drive and mtx (http://sourceforge.net/projects/mtx
) to interact with the robot. Then whatever you choose to use should connect through those.
I would dump Windows in a New York Minute. But then I'm not in your shoes and I don't have to deal with your colleagues and bosses. You'll have to make that call for yourself.