Except that this isn't using MathJax, at least not directly. The link
you give is to integrating the CodeCogs LaTeX equation editor with
CKEditor, which gives a button-based LaTeX editor. The default output
for the equation editor is a GIF image, so what this is really doing
is giving you a way of embedding the GIF in the web page. The editor
does give you LaTeX expressions in its text field, but then you would
need to paste the LaTeX into the HTML and configure the script tags
for MathML separately in the HTML page. I don't think any of this
directly addresses the question. It's kind of handy as a LaTeX
editor, but doesn't really give MathJax integration. However, by
using a few DOM calls, you can get the value in the textarea field of
the LaTeX editor, wrap it in LaTeX delimiters, and paste it into the
innerHTML of a div or something like that. None of that is done in
the plugin you linked to, though. The plugin just inserts the
generated GIF.
The short answer to the question is "no", there is not (yet) a way of
integrating MathJax with CKEditor. It is an interesting idea, and the
integration question has come up in reference to the tinymce editor
before, but for the moment, the CodeCogs LaTeX editor is not built
around MathJax, it is built around generating a GIF and embedding
that.