It seems you'll need to buy their own products, If that's the case I can see why you want to use a different solution.
If you're able to access the drive using Windows File Share (CIFS, SMB or SAMBA) methods, you can back up the device by pointing your server to the UNC path \\SERVERNAME\SHAREPOINT. You won't get the performance benefit of the agent, but it will not be as bad as you think. You could make a sharepoint that can only be accessed by one machine under one account. Then make a job that uses this special set of credentials to connect to the sharepoint. You won't be able to get the device settings (the equivalent of Windows' System State) but you can usually export the config to a file on most appliances, perhaps this one will as well. If you did that on a monthly basis, you might be covered. It's worth discussing with your team.
If the methods of access are not Windows Based, there is a Unix Agent that can be purchased for BUE. You could set up BUE 11d on a notebook in 60 day trial mode and with the Unix capabilities enabled, attempt to back up the device without an agent. It still might work, and it's worth a shot. This would tell you if it's worth buying the agent.