Both are using a different SCSI sub-address. The tape is using the usual 'lun 0' and the robot is at 'lun 1'. This requires that your kernel is built with SCSI LUN support in addition to the standard SCSI support. In order to operate the robot you will also need to install mtx, the SCSI Media Changer and Backup Device Control System.

For the actual backup software I would recommend AMANDA on Linux. AMANDA allows you to set up a single master backup server to back up multiple hosts to a single tape drive.