Well, DukeNuke2, it appears to be one of these. I re-seated the drives in question and booted from the DVD I used for the O/S install and when I dropped to a prompt it was able to see the drives in the format utility. I relabeled them and booted single user. At that point devfsadm was able to add the paths unlike before and now they are usable under the O/S as expected.
I didn't know the 440 drive plane was so temperamental! Now I've successfully created my first multi-disk ZFS pool and things are looking good. You were a huge help!
Thank you, thank you, thank you!