According to various posts, it should work, but it just isn't supported by Cisco. As mentioned by alegalle at the thread here, it should work as long as Intel VT-x/EPT (and equivalent on AMD processors) is enabled. Just keep in mind that new features and versions are not currently tested on Hyper-V, which means your installation could break in the future.
I asked for a road map of features coming to VIRL. I will be spending about $4000 once I add the Essentials Kit to use all 24 logical cores.
My HP DL360e Gen8 Server
HP DL360e Gen8 Server Dual Intel E5-2430v2 6 core CPUs ( VIRL shows it as 24 cores, 12 physical)
4 NICs onboard
P222 SAS controller and two SAS drives
dual power supplies
15 month HP 24x7 Warranty left on it.
HP dual NIC card
8GB SDHC card in the SD slot on motherboard
I downloaded Standalone VMware 6 eSXi and installed it. The Essentials Kit ($560) gives me all the cores for each VM.