To detect if player 2 is a computer you can put a player 2 unit next to a gaia unit and use a trigger to detect if the gaia unit becomes owned by player 2. Only some units will do this (you cant use wolves because they will stay as gaia). Horses are good to use because not only do they change ownership but they have a small line of sight so you can pack all of your player/cpu detection horses into a small area on the map.
Does anybody knows of a better method than this?
"What doesn't kill us makes us stronger." -Friedrich Nietzsche