No, nick- if you go and thoroughly read the skill description of grand cross, you are required to take a certain amount of damage. But if you have the proper reduction gears, you do not take the additional damage. Go use grand cross with the right redux gears, and watch your hp, and the numbers that fly above your head. You will take damage according to whats necessary, but not anything additional (Or if you only reduce x amount of the three holy hits on yourself, you still may take some extra self damage).
Did I describe it well enough for you to get ?