Limited configurations are supported for VMware HA and ESX Server 3i hosts
Details
VirtualCenter 2.5 Update 1 extends support for VMware High Availability (HA) to ESX Server 3i hosts, but currently requires some additional restrictions: swap space must be enabled on individual ESX Server 3i hosts (KB 1004177), and only homogeneous (non-mixed) clusters are supported at this time.
Solution
Homogeneous (non-mixed) clusters are fully supported when composed entirely of non-ESXi hosts, or entirely of ESXi hosts. More specifically:
Homogeneous cluster of ESX Server 3.0.x hosts or ESX Server 3.5 hosts or ESX Server 3i hosts are supported.
Heterogeneous cluster of ESX Server 3.0.x and ESX Server 3.5 is supported.
Heterogeneous cluster of ESX Server 3.0.x, ESX Server 3.5, and ESX Server 3i are currently NOT supported.
Virtual Center 2.5 Update 2 extends support for Heterogeneous clusters of ESX Server 3.0.x, ESX Server 3.5, and ESX Server 3i.