If you are planning to deploy Exchange Server 2010 Database Availability Groups, and you virtualize your Exchange environment, then it is important to understand the supported scenarios.
Microsoft makes it very clear in their system requirements for Exchange Server 2010:
Microsoft doesn’t support combining Exchange high availability solutions (database availability groups (DAGs)) with hypervisor-based clustering, high availability, or migration solutions that will move or automatically failover mailbox servers that are members of a DAG between clustered root servers. DAGs are supported in hardware virtualization environments provided that the virtualization environment doesn’t employ clustered root servers, or the clustered root servers have been configured to never failover or automatically move mailbox servers that are members of a DAG to another root server.
In short, DAG members should have any virtualization high availability options disabled.
This is in slight contrast to the advice from VMware themselves:
While the use of database availability groups on top of hypervisor based clustering is not a formerly (sic) supported configuration, internal VMware tests have shown that the two technologies can co-exist and can be a viable solution to ensure maximum recoverability in the case of a host failure.
To paraphrase, it isn’t supported but we think you’ll be fine.
You might get some push back from customers or managers who have been sold on the idea of VMware HA for everything, or who take the line from VMware as implied support for the configuration. But in the real world I prefer to go with what is supported over what is possible.