On my quick test on a single node on 5.8 CENTOS, the cluster install within the HMC fails when I don't have a host entry with my ip address of the machine. Thus, you will have to at least make changes to the etc/hosts file. Try the following:
-stop the hmc service (service hmc stop)
-uninstall puppet which will also uninstall hmc (yum erase puppet)
-get your current ip address (ifconfig)
-add that ip address to your etc/hosts file, the example content of my file is (my example ip 10.10.10.157):
# Do not remove the following line, or various programs
# that require network functionality will fail.
10.10.10.157 localhost.localdomain localhost
127.0.0.1 localhost.localdomain localhost
::1 localhost6.localdomain6 localhost6
-reboot the machine
-execute a "ping localhost" to verify response and the ip address shown is the one you entered in your /etc/hosts file.
-you also may want to ping outside to verify you can connect to the internet if you aren't using a local yum repository to install.
-Once all the above is verified, proceed installing hmc (yum install hmc)
-Once hmc is installed, proceed to the HMC page and follow the prompts to execute the minimal install (HDFS, MapReduce, Ganglia, Nagios)
Let us know if that helps.