6.0 is 6 versions out of date
the current in the 6 series is RHEL 6.6 , with RHEL 7.0 as the CURRENT .
Also you MUST BUY $$$ the required support contract
for a server install on a cluster
contact redhat sales
depending on the nodes the license could be a few thousand PER YEAR
use the FREE rebuild CentOS 7.0
or the bit older CentOS 6.6