Hi Ian,
So I just tried it out myself. The file that is pulled off is actually a zipped up directory, even though the filename ends with .cfg. If you're looking to take the config off of the NetSight server, you can download the file and rename it to .zip and then unzip it with your favorite utility. Within there, the xml configuration file as well as a couple other files will be available. If you choose to look at the file from NetSight, either through Inventory Manager or comparing backups via OneView, the server will show you the correct config information.
I'll follow up with development on this, as the .cfg extension is a bit deceiving.
Let me know if that solves your problem. I verified this on NetSight version 6.1.0.124 with a Summit X460-24p running 15.4.2.8.
Thanks,
-Tyler