After a very quick glance at some of the SL500 documentation, it seems that there are no drivers for that tape library.
You install drivers for the HBA's that are in the computer that connects to that library then you follow the User Guide to administer the beast. External peripherals rarely need drivers (for example, you don't install drivers for monitors but only for your graphics cards).
The SL500 documentation is here:
You can freely download and save all the PDF documents for future reference.
The User Guide is probably a good start point.
Considering how complex and expensive that tape library is, you surely have a maintenance contract that covers it. Go log a SR with TechSupport for further assistance.
I am quite sure that since you mentioned Microsoft Operating Systems in your first post, you can get drivers from HP for those HP Ultrium drives. You can go search over there at HP. I choose not to do that for you. Then when you remove the Ultrium drives from the library, you will be able to directly address them.
As long as the drives are inside the physical library, you need to address the entire functionality as described in the library documentation I referenced in my first reply. There would not be any direct hardware connectivity to the drives as long as they are inside the library chassis.
I think you now need to find some HP forum or a Microsoft forum for further guidance since it seems you don't want to use the library as it was originally created.
Reaad DocID 1020221.1 on support.oracle.com.
Driver for Microsofts DPM backup software available on support.oracle.com (link provided at this Docs).
For other software you should use the generic "Unknown Medium Changer" driver that comes with Windows...