I have had the site read up every once in a while, but the mechanism it uses will probably need some tweaking do to the change in the server.
On the other hand, the page source will always reflect what is displayed. So if it did display "UP" the source will replace the appropriate index.png with the up.png. PHP allows the web server to dynamically generate a static page. So you wont see the effects of a change until the page is refreshed and the cache clears.