A hero in a unit. Can you attack a hero in combat and split attacks between the unit and the hero? Do wounds inflicted on a unit pass to the hero, e.g. the unit has 5 models with one wound and one hero with 3 wounds, 10 wounds are inflicted, what happens to the remaining 5 wounds? The remaining 5 wounds are lost or are they transferred to the hero? If the wounds go through, does the hero's DEF matter?
Once the hero joins the unit, he becomes part of it like any other models. Unless your attack specifically targets an individual model (like sniper rifles), the attack is made against the unit, not the hero. So you use the defense of the unit, and the wounds are applied first to non-hero models until they are all killed, and then they pass on to the hero.