Yes, people using Contribute CS5 will be able to make updates to the site. But, if they administer the website in Contribute CS5, then, you will not be able to administer the website using Contribute CS4. For more information, view the following link, http://blogs.adobe.com/contribute/2009/09/compatibilty_transition_mode.html.
But the post you linked to doesn't address the problem that was asked. That post says you can edit a site with an older version of Contribute than the one version that site is Administrated by. e.g. Site created and admined by CS5 but user can edit with CS4 or CS3.
The questions was about the reveres... and is actually the problem I am having. I created and set in CS4. But now I have clients with CS5 and they workflow feature isn't working correctly. Is this a known issue? Is there a fix or does the admin have to be on the highest version of Contribute being used for that site?
Can you tell me what is the workflow issue that the users are facing?