The answer is sort of. Strictly speaking it is possible. You can indeed enable the Hyper-V role in a Server Core installation of Windows Server 2008 and Windows Server 2008 R2. I’ve done it on both OS’s on both VMware Workstation 6.5 and on Hyper-V. Logically this means you can deploy Hyper-V Server 2008 and Hyper-V Server 2008 R2 in a VM.
You can even create VM’s on the hosts. However, the hardware requirements are not passed through to the VM’s and therefore the hypervisor never starts up. That means you cannot start up those VM’s.
Why would you care? You certainly cannot do it in a production scenario. But you might find it handy when doing some demos, lab work or testing of clustering or VMM.
I have been told (but I have not tried this so I cannot say it will work) that you can get Hyper-V to install and run in an ESXi 3.X virtual machine. The performance is said to be awful, but might be useful for a lab with limited hardware.