Hey,
when you run the appliance on a host inside a HA-cluster, the vCenter is protected by HA, as HA runs (once it its configured using vCenter) fully on the hosts and doesn't need vCenter to work.
Unfortunately, the clustering solution vCenter Server heartbeat only supports the windows installation of vCenter Server right now.: http://www.vmware.com/products/vcenter-server-heartbeat
Regards
Tim