Based on the rest of #1, I think your main point is: do not use ONLY hardware RAID for the boot drives, that slapping the extra layer of redundancy (via the mirrored ZFS pool) will make dealing with upgrades a whole lot easier.1. Don't use SVM for your boot drives.
Yes, excellent point, and one that I actually learned after my initial post: for numerous reasons (including the live upgrade scenario that you mention), it is never good to run the Oracle software on the same filesystem as the OS.2. ...You do NOT want home directories located on an rpool within a live upgrade boot environment.
My RAID controller does indeed support RAID-6, so I'll go that route. But re: using ZFS only: I've been burned by having 'software RAID-only' (the database files on mirrored ZFS pools w/no RAID parity): last year, a power outage (combined with a usesless UPS) irrevokably corrupted the ZFS data pool: fortunately it was not in production, but I had major egg on my face: my x-86 server was the only one that had problems - all the Windows and Solaris HW RAID servers came back on line just fine. This left me wary of any 'ZFS-only' configurations...anecdotally, among my limited peer group, I have come across nobody willing to put all their eggs in the ZFS basket.3. ...otherwise I'd use ZFS and not bother with SVM