It depends. If the other websites are similar or have the same interest than the "1st" one, and are benefiting the same owners, then no. it would be considered as "Abusing the Ad Network". What Google wants is to have one website to enter a bid for one keyword. If the other websites are your competitors or other clients you may manage, it's ok. If they are all websites from the same client, there is a risk of having the ad account suspended.