CentOS 4 Offers Strong RHEL Alternative - page 5
There are some apps that you may want to use on CentOS that for whatever reason need to know that RHEL 4 is installed. Thanks to the CentOS community there is a "fix" for this that will make apps think that you're actually running "the real thing."
All you need to do is add a line to the /etc/redhat-release file. The default (type cat /etc/redhat-release) reads CentOS 4.0 (final). Just add "Red Hat Enterprise Linux AS release 4 (Nahant)" and you're likely good to go.
Your file will look like this:
root@localhost ~]# cat /etc/redhat-release CentOS release 4.0 (Final) Red Hat Enterprise Linux AS release 4 (Nahant)
If all you have in your enterprise was a few (say less than 5) servers and you are (or have) a solid technical understanding and don't need additional support (beyond mailing lists and forums) than CentOS is likely a good choice. Certainly the fact that CentOS 4 isn't "certified" for RHEL 4 applications in particular Oracle is also a consideration (if that's your database).
CentOS 4 is currently available for i386, ia64 and x86_64, while RHEL4 is available for those as well as IBM zSeries, POWER series, and S/390 series systems.
When you pay for Red Hat Network, you also have the option of getting Red Hat Network's Management and Provisioning modules that significantly improves an admins ability to properly handle multi-server medium enterprise deployment and management. (Here's a chart on those features.) Certainly if you're running a small shop it's a bit of overkill, and there are always other alternatives (though I don't know of any for Red Hat that are better or easier than Red Hat's own).