Yes, you can install one without the other. The easiest is to use yum's groupinstall feature either with a properly configured local repo and/or with rhn if the systems are registered.
Code:
yum groupinstall "Cluster Storage" "Clustering"
yum groupinstall "Virtualization"
You can get the names of the groups with
yum grouplist to confirm that my examples above are using correct names as I am going from memory on the group names.
