the way i understand that part of the description is that, you gain the max health up, but it's not filled. say if the battle keeps going, and you annilated a gk and a baze (two toons with high health), and THEN you have a chirrut or barriss still alive and does the equalization move. Theoretically your DN will now have a MASSIVE health pool
but honestly in practice this never matters, since DN himself can't health steal fast enough to ever fill the possible substantial increase in Max HP he gets. and if your battle has gone so long as for him to annihilate multiple foes and have someone health equalize for him, then it's not like your squad really needs it either