VMware has done a great job in recent versions of Fusion, Workstation and vSphere when it comes to allowing users to run other hypervisor applications inside a virtual machine. In fact, many of my recent blog posts here at virtualizationadmin.com are using Hyper-V servers that I have running under VMware Fusion 5.
To enable this feature inside one of your virtual machines,
- Make sure the virtual machine is in a powered off state
- Open that virtual machine’s properties page
- Select the Processors & Memory page
- Select the checkbox next to Enable hypervisor applications in this virtual machine
- Restart the server
Once this support is added, you should be able to, for example, install the Hyper-V role on a Windows server.