Did you ever figure this out? We have a new System Tech that needs to be able to upload CSV into the inventory preload but not be able to delete the information. I've tried giving full access to the account and omitting the delete the permissions and it still just spins when trying to upload the CSV.
I was just working on this. This wont be EXACT but close enough.
Inventory Preload Records ALL
Mobile Device Extension Attributes ALL
Mobile Devices ALL
User Extension Attributes ALL
I dont know which exactly made it work but it worked once I set these.