The AI doesn't build elite barracks in death match even, don't know why.. The heroes are only recruitable in the world map, cause it's like a war with many different armies, so if Idrial for example is in one location, she can't be at another map fighting a battle..
The AI forfeits when it finds it impossible to beat you.. There are some maps that you can defeat their base, but neither they can hurt you.. Sometimes, this could end up in a forfeit from the AI. so be patient..