There's also the question of how much time the "parents" will be willing to expend on training the dragon; if they're anything like normal humans then they'll likely have to hang around and give the little wyrmling a lot of attention, which would get in the way of adventuring. Of course, they could take him along on their adventures once he hatches, but you'll have to ask yourself how the people they meet will react to them raising an "evil" dragon.