The advantage of hanging a corner ground on that delta is you don't need to add a conductor. Just put white tape on the grounded conductor. You needed an EGC anyway so that should be there. I would have had a problem approving an ungrounded delta in the first place unless the installer had a compelling reason. Usually this is going to be the heaters in a glass plant or something. Even then I would want to see non-critical supplies grounded. Like you say, spooky things can happen.
