A non-tamer would have to have magery or chivalry to heal it but there isn't anything really worthwhile to use without taming. I believe that you can have pets like dogs, cats, chickens etc but they would all die very quickly. As a non-tamer you can ride a swamp dragon and use the armor to absorb some damage. I believe anyone can control a lesser hiryu but I have no idea if it can do much damage without taming skills.