So I went ahead and installed Debian 9 after unplugging all my RAID drives from the MB. The only hitch I had was that once I installed from bootable USB, the boot loader was always pointing to the wrong drive. I got past it by editing the GRUB config on boot (press the "e" key on boot screen). I had to set the booth pointers from "root=/dev/sda" to "root=/dev/sdb". Tried editing fstab, but I just got a lot of errors. Maybe I ran into errors because I'm using a hardware raid controller for the system drives (2 SSD drives)
As a last resort, I did:
# grub-install /dev/sda1
I'm not sure if this fixed the GRUB loader to look at the SSD drive, but it does now load properly.
I then went through the process of installing OMV4.
After this, I just pulled up the web GUI and was able to login just fine.
NOW, I shutdown, plugged in all my RAID drives again and booted up again. All my drives showed up and RAID status was clean.
So it looks like I'm good to go. Thanks for OMV, it's great.