Like this other situation. You want it to be fair, but how fair would it be if:
Player A (WHM) Joins a dungeon for gear and player B (SMN) joins a dungeon for seals. A WHM piece drops and player A rolls need on it, then a caster piece rolls and WHM rolls on it aswell and happens to win it for an alt. Player A gets all loot while player B gets nothing while each of you joined the dungeon for your own purposes, but somehow you decided yours is more important for whatever selfish reason. Is that fair for you?