What you laid out is my understanding as well with the caveat that you can’t do a full block level backup, that sort of functionality is reserved for NAS to NAS, only.
I would strongly recommend doing the backup with an USB drive.
It is not “easy” to mount/unmount a storage pool/volume to safely eject and later reinsert the pool/volume.
When using an USB drive as backup medium, Hyper Backup can automatically eject the USB drive after it has finished the job.
And as pcmike stated, you have no benefit when using a “internal” volume as backup volume.
In summary an USB drive is much easier to manage. You also haven’t to worry about speed issues when using an USB drive, because your DS has USB3. Just be sure not to use an SMR drive as a backup drive, because they get slower and slower the fuller they get. And the integrity check can take forever when using a SMR drive.
Greetings
Oliver
PS: Are you sure you mean RAID0? In this case the Hot Spare is useless. When one drive dies in a RAID0 config, all the data are lost immediately. And today’s HDs are fast enough to saturate the LAN connection(s) of your DS, even when using SMB multichannel (with RAID1/RAID5/SHR1).
I know this video and just rewatched it. The crucial difference is, that in this context Will is talking about an onsite backup.
But even for an onsite backup I would recommend an external hard drive, because this is more flexible. When you need more space you can just add another hard drive in the empty bay, without the need to reconfigure the backup process.