yes, any hired henchmen will be given the same amount of exp that the main character that you are using to talk to the henchmen vendor. But in order to do this, first dismiss the hired henchmen when you first get him ( he will spawn in the hall of heroes) then hire him again. He will now have the same exp as whoever talked to him (i think). So even if you store him in the hall of heroes and have a 5 lvl gap later, just talk to him again and he will be leveled up to the same level with the same amount of exp.
