ReReplacer should work on any page rendered through your Joomla website.
But it only works in the HTML output that is rendered through Joomla (and passed through the plugins).
If your site is loading content through javascript/ajax (so that the page does not load fresh), then generally the content is grabbed as is and not passed through the Joomla plugins.
So to know the answer as to why it is not working, I would need more information.
And/or see it online in action.