UEFI Remote Mangement

UEFI shouldn't add any efficiencies all by itself, since BIOS and UEFI are there to bootstrap a system from bare CPU to an OS, and provide a translation layer between the OS and the hardware once things are booted. UEFI has a lot more capabilities in this regard.

It is entirely possible that VMWare (and the other VM vendors) will develop a hypervisor that runs directly from UEFI. Right now, it launches the hypervisor the same way it would a normal OS. Would running directly in UEFI be more efficient? Possibly, though probably not by much.

Well, after much searching, experimentation, and general frustration, I have basically come to the conclusion that Hyper-V does not currently support UEFI guests, even if the Hyper-V server is running in UEFI configuration.

This seems to be supported by the fact that that recent builds of Windows Blue have what they call "Generation 2" VM's that include UEFI support, based on this article:

http://www.chris123nt.com/2013/04/23/windows-8-1-blue-build-9369-hyper-v-uefi/

Sad really that there's been so much misinformation about this floating about, with so many people insisting UEFI works for guests, but I can find no way to make that happen.

EDIT:

Since this question was asked, Microsoft released Windows Server 2012 R2, which supports the Generation 2 VM's, which do in fact support UEFI for guests.