Banning a user because he was using black hat seo

Hi all

One my users was using black hat seo and i banned the user. He had his own website domain mapped, and was using the supporter plugin. My question is if google blacklists a particular website, does the entire network get affected because all the sites would be under one ip? I was lucky to spot this because our network is small at the moment. When the network does get larger, it would be very difficult to spot this kind of users.