(OK, so finally well enough to remember how to type… 
)
BLUF (Botton Line Up Front): I think I have a tested, proven, and practical solution to the issue.
Turns out that using VirtualBox was a very dry well, and I lost a couple of days trying to make it love me… erm… make it love the idea of multiple disk drives. Rockstor installer would see all the volumes and install in the first/designated OS drive just fine. But after installation was complete… nothing. It only saw the install disk from that point forward. Tried several combinations of drive controllers, and always the same thing - VirtualBox and Rockstor by itself works, but it only recognizes the first volume and just won’t pick up on any others.
So I packed it in, had another think, and remembered that as a self-deluded IT professional, I have resources far beyond those of normal users. I have access to a Broadcom support account thanks to my employer (I do VMware stuff professionally) so I was able to grab a copy of VMware Workstation Pro for gratis. This knowledge could come in handy someday so I suppose it’s business-related, if observed from a suitable distance in dim lighting.
But I digress…
VMware Workstation installed and running. Created a new VM with a 20Gb OS disk and a handful of small 5Gb disks. Installed Rockstor and rebooted. BEHOLD! All drives are visible now (yay!) but there’s a lot of error messages about how every drive has the same serial number. Shut down the VM, edited the .vmx file and added in the clause disk.enableUUID = "TRUE" and started the VM. No complaints now, so let’s build two pools of equal size and (because I’ve learned my lesson) label them pool01 and pool02. Then SSH into the VM, and use the command:
btrfs filesystem label /mnt2/pool02 pool_two
Back up configs, hold my breath, and trip the VM. Which comes back up, but pool02 is gone and isn’t in the /sys/fs/btrfs directory either… Start to panic. Reload configs, realize that the drives are still there even if the pool isn’t, switch to the Storage|Disks tab in the UI to take a look.
The drives are all there and several are flagged that there’s already a BTRFS filesystem present and would I like to import it? Thanks, and I believe I will do just that…
And pool_two appears in the pool list, all drives and shares in place. Think we’ve got a winner here. I’ll have to use the “by-uuid” approach
Also: Ordered a new UPS from Cyber Power Systems that’s NUT compatible and I’ll set it up as soon as this pool situation is sorted. Lesson learned, @hooverdan. The whole “which pool is you?” situation here may be interfering with my ability to create a new service account to drive NUT, and also won’t allow for updates or installation of new RockOns. So it’s in DOU (Dumb Old UPS) mode right now, but I’ll sort that next.
TL;DR (Too Long, Didn’t Read): I think this may work on production. I’ll try that next and let you know how it turns out.