In the document with the virtual host configuration file http://doc.ez.no/eZ-Publish/Technical-manual/5.x/Installation/Virtual-host-setup/Virtual-host-example there is a rewrite rule for robot.txt,

        # Give direct access to robots.txt for use by crawlers (Google,
        # Bing, Spammers..)
        RewriteRule ^/robots\.txt - [L]

However there is no robots.txt file in ezpublish