I have successfully installed ArcGIS Server 10.1 in CentOS 6.5 recently.
Steps are as mostly the same as installation in Linux, please see:
Before installation, better to follow the steps below:
Give your host machine a good hostname, don’t use @, .(dot), etc special characters
Configure your hosts file, make sure your hostname is accessible through the domain network
Cent OS version should be 6.5 and above: cat /etc/*release*
Follow the steps in the guide, in step 6, using online Authorize method, and you will be required to input authorization code obtained from ESRI and your contact details.
After authorization, the arcgis/manager website should be available on firefox, and hence installation for this current user is done.
Configure ArcGIS for Server to be started with the operating system, treat Cent OS as RHEL.