I know that RHEL is free for the source version. I also know that CentOS uses that to get thier own distro together, that was my point, CentOS is RHEL for all intents and purposes when it comes to 3rd party commercial software.
The 3rd party may not support CentOS officially, but they do not need to be told CentOS, you can tell them RHEL and get a real usefull response to issues with their product.