How to migrate Enterprise Vault to a virtual environment is a question that comes up frequently these days. Many, many customers run EV successfully inside a virtual machine. Sometimes people use virtual machines simply so that they have the flexibility of moving the machine between physical machines more easily, sometimes it is so that hardware resources can be shared across multiple applications.
Whatever the reason for doing it there is a good whitepaper from Symantec which is worth a read. Here is the link.