Each cluster is configured with a minimal CPU type that all hosts in that cluster must support (you specify the CPU type in the RHEV-M GUI when creating the cluster). Guests running on hosts within the cluster all run on this CPU type, ensuring that every guest can be live migrated to any host within the cluster. This cannot be changed after creation without significant disruption. All hosts in a cluster must run the same CPU type (Intel or AMD).
Red Hat, RHEV/3.6, RHEV
Live Migration of VMs, VM Mobility, VM Mobility and HA