General redirect question

Yes, you should be able to do that. If you check the web.xml of XWiki you should see:

  <error-page>
    <error-code>404</error-code>
    <location>/bin/view/Main/DocumentDoesNotExist</location>
  </error-page>

This means that you can edit this page and modify its content to do a redirect.

Actually there’s also a docdoesnotexist.vm template file that you could override through a custom skin. But it’s more involved. I’d recommend creating or editing the Main.DocumentDoesNotExist page.