ungrounded delta primary ?

[tortuga]

This system is sounding like what I saw referenced on google as a SWER (Single Wire Earth Return) when I was trying to figure out what I was looking at. Any Experience with any additional safety concerns beyond the normal considerations if this is what I am seeing? Seems to me it could have a real impact for pool bonding safety if not done correctly. Seems too that this type of system would have a higher incidence of stray voltage or NEV complications in a house.

With a MGN when you loose the combined neutral but the primary stays hot thats when strange things start to happen, in a sense they are all part SWER if the primary side is grounded.
A MGN in perfect condition can be near a pool and still affect it, lawyers call it 'electrical trespass'.
If it were up to me with overhead I'd keep the primary ungrounded, use branch protection and use advanced SEL relays like these:

https://selinc.com/products/751/

These days though cost is a huge factor and here on the west coast were looking at moving lots of old distribution underground as every time a primary fuse blows it tends thow sparks and causes these fires were having, and its pretty attractive to be able to use one concentric MV cable to loop feed a entire subdivision.