This set up is not corner grounded, its all motor load, but it does read voltage phase to ground on the output side. I am just trying to wrap my head around the "how does it have a ground path" if it is not physically connected to ground on the output side of the XFMR.
On the output side, the only possible fault current is from line to line when the delta is not grounded.
The first fault from anywhere in the circuit will NOT cause fault current to flow. It will just establish a ground point in the circuit.
It is the second fault that will result in fault current, and that fault current will flow from one grounded point in the delta to the other, completing the circuit through the windings.
Grounding the XO on the input side will have no effect one way or the other since that has no path to the delta side.
When you read stable and balanced line to ground voltages on an ungrounded (as far as you know) delta, you are usually seeing the effects of a capacitive voltage divider among lines and ground. It will not provide significant current and will not show up as line voltage with a wiggy or low impedance meter.