If you want to play an Aiel, the max you could command/control is one clan. I'm definitely willing to allow liberties- the only restriction is that you cannot 
[hider=SPOILER!]help Aemon in his last battle against Ba'alzamon's forces, over the river.[/hider]
The Aiel suddenly appearing would definitely cause the Shadow forces to retreat if they could, but that's not always an option- it would more likely cause a fight to the complete demolishment of one side of the battle.