Use product X as a smart proxy server
This gives us a solution to:
Being able to control the domain that the concepts site is on.
We will be able to control how we register the site with Google search indexing.
We can control getting analytics we can on the site.
We retain all of the convenience we have with Confluence
We can even look at modifying the branding later
We can unit test the solution
Using Product X as a smart proxy server means doing this:
User Web browser ← HTTPS → Product X ← HTTPS → Confluence
Product X can modify the content of the HTML on the fly to change links from say interfaceware.atlassian.net to concepts.interfaceware.com etc.