Hi,
This is definitely outside of normal Veeam conversation but happy to jump in and help.
You haven’t mentioned if you have a RAID controller or not, are you using a hardware RAID or software RAID?
If hardware, you can create your RAID 10 and then present two partitions within this, you would then create a mount point for your second partition and you’d be good to go.
If software, you need to create the partition in advance. The problem you’ll have is you need to create the software RAID prior to installation if you wish to put your OS on the software RAID.
The tool you’ll need to create software RAIDs is mdadm.
If you’re using software RAID you’ll be out of luck getting any official support for RAID 10 as /boot can’t use any software RAID other than RAID1. (Installation/SoftwareRAID - Community Help Wiki (ubuntu.com))
Let us know if we’re talking software/hardware RAID and we can help further hopefully.