Interworx in clustering mode will allow you to have one (or more) servers host web sites and another (or more) servers host email+dns. However mysql runs only on the master node (which also is the load balancer) and cannot be run on a separate machine (and be controlled through the control panel).
Our clustering setup works a very specific way. And to clarify: the Cluster Manager is also the MySQL server. All HTML and mail data are physically stored on the Cluster Manager but the load of the web traffic is shared across all servers according to your LB policy.