If you're worried, why not just use a delta-wye transformer, ground the secondary neutral, and just not run a 4th wire? If you don't have to worry about phase shift, it's really the way to go.
Though the coils in a delta secondary aren't grounded, the core is, and magnetic core conductance and reactance will hold a delta secondary near equal potential, especially if the phases are balanced. Think of it like a wye-wye with a high impedance ground on the neutral.
