This problem does't only happen with WP-O-Matic, it happens to auto blogs which doesn't spin the content, obviously you may not want to spin your content for a number of reasons, so if you add a simple page / bit of text explaining to webmasters, if they don't want their content on your blog, to send a e-mail to a address (Which you check daily) explaining so, then remove their feed and reply explaining you have done so, problem sloved.