The question would be if they just grabbed a static snapshot of the site and are using that or if they are actually still pointing back to some of the stolen si

The question would be if they just grabbed a static snapshot of the site and are using that or if they are actually still pointing back to some of the stolen sites files. If they are pointing back to the stolen sites JavaScript files then yes it would be very easy to redirect the traffic back to their site. Given that the code resides on their server they are completely within their rights to do so as well. I would also minify the JavaScript file as well, so the change is not immediately apparent to them. Make them work to figure out why the code they have stolen is not working.