Not sure if this meets you definition of cluster or not but all of our IdM servers are VMs. We have a multi-master set with standard replication. I have IdM servers 2 in one location with 1 serving as DNS CA, LDAP, etc and a second serving SMB shares and backing up the LDAP services. Across private links in to another location/facility we have a second master with the full suite of services installed and used. We do not use AD so the level of complexity compared to mixed environments is low but everything works fine for us.
Jeff