They do on EB on BI with ferromancer's installer. They invaded Corsica quite early in the game, though only with 2 units. I didnt see how much they did it later as i switched to EB on Alexander as the battlefield AI on it is a bit better. If you could just combine BI campaign AI with Alexander battlefield AI that would be nice - maybe in EBII it'd be possible with modded Medieval II AI - i don't know (not a modder or even close to understanding it)