in that spirit many (ie dell) servers come with dual SD slots to run ESXi...... so certainly we could use the same principal with 2 of the mentioned usb ssd in a zraid or mdadm raid... or make an occasional manual clone of the usb and keep a cold spare on the shelf - even better than raid. you could have a 3rd usb (ie normal flash drive), where you rsync the pve confs to nightly, this would be a solid solution assuming his install is not mission critical needing 5x 9s... if that were the case you should always run real raid on a real raid card with raid1 or raid10 of high quality ssd or sas drives..