FYI - I think a RDM can cast Black magic(spike series) +White magic(stoneskin/blink/phalanx) and RDM can equip "fencer+shield".

But Red Mage is a hybrid mage - uses both white (healing) and black magic (elemental dmg).
IMO the "caster tank" I read from OP is not a Red Mage. ^^;