You know your kids best, so as long as you know there not going to be running wild or "sneak" out of the room to go somewhere there not suppose to be while your gone id see no problem with it.
Before you go out of course just set ground rules, like that they should stick together if allowed to leave the room and how far they can go, can they goto the pool, arcade, or food court? and if so what time should they be back to the room. And of course remind them of what to do incase of an emergency, i know its disney, but things can happen. Just remind them that the front desk is there to help if they need it, and be sure to carry your cell phone with you. Just periodically call and check up on them. Im assuming if you consider it then you trust your kids so go for it, you deserve a night out!