I've just spent troubleshooting this for 4 days, but finally realized where I went wrong. It was the order of things. I wanted to change the boot pool name from "rpool" to "spool":
1) Install proxmox, boot it
2) Login and edit most files containing "rpool" in /etc and /boot. I used "find /etc -type f -exec grep -H 'rpool' {} \;" and "find /boot -type f -exec grep -H 'rpool' {} \;". That lists all files, edit each one, except the grub lock files.
3) proxmox-boot-tool refresh
4) Reboot, boot the proxmox installer in debug mode (advanced - graphical debug), press Ctrl-D once to skip first stage
5) "zpool import" lists all your pool including rpool. "zpool import -f rpool spool" to rename, "zfs list" to verify, then "zpool export spool".
6) Reboot into Proxmox and it now works, running from "spool"!
Thanks for the info above!