You have got it right, as far as Grounding a Closed or Open Vee Delta Secondary.
Either pick one - ONLY ONE - Line Conductor / Transformer Terminal, and make it the Grounded Conductor,
Use the Center Tap of "The Center Transformer", and bond it to Ground + Equipment, then bring out an EGC (Equipment Grounding Conductor) from the Transformer to bond the downstream equipment.
Advantage using the Center Tapped method:
Lower Voltage to Ground than with a Corner Grounding Scheme (either 120V to Ground, or 208V to Ground).
Also, if using 1 Phase 2 wire equipment, placing these loads across Lines A and C (assuming Line "B" is the "Top of the Triangle" / "Stinger Leg"), will allow the use of Circuit Breakers with Single Pole Fault Ratings at 120V (the most common breakers).
The Corner Grounded setup would need breakers with single pole fault ratings at 240V minimum - for 1 Phase and 3 Phase connected equipment / loads.
Same goes for 3 Phase loads on the Center Tap Grounded setup.
Advantage for the Corner Grounded setup:
Full sized Grounded Conductor bonded to the entire Ground Bonding scope (star point).
Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!