I think that makes sense given that onedrive is a cloud-based storage service with some locally cached data and pointers to the cloud data. If the file is not persisted locally, then there would be nothing to copy to S3.
Not that I'm aware of. Normally I would just suggest you use our Office 365 product to back up data in OneDrive. I'll do a little more digging this afternoon see if I can find a solution for you, but right now I don't know of any.