@technot when you say performance was a bit on the low end when dom0 handled the drive, how low compared to when the controller is passthrough?
For ZFS, it is still good with few number of disks but the performance won't be high than raid10 until you have more vdevs (which means striping across multiple vdevs). You do need to passthrough the disks to dom0, so you'll have to destroy the raid as you mentioned and the more ram the better for ZFS, usually around 1GB per 1TB of storage for good caching performance.
One thing to note, you can't use ZFS for dom0 yet so you still need another drive for XCP-ng.