Why would the situtation with the transformer be any different.
Alternating-Current Systems to Be Grounded. 250.20(B)(2):
If the neutral conductor is not used as a circuit conductor it does not have to be the conductor that is grounded. It is usually wise to still use it as the grounded conductor if that is possible.Where the system is 3-phase, 4-wire, wye connected in which the neutral conductor is used as a circuit conductor