Q: Two unknown devices on my Windows Server 2012 R2 Hyper-V virtual machines (VMs) aren't running Windows Server 2012 R2 guest OS--is this a problem?
A: This is actually normal. There are several new features to Windows Server 2012 R2 Hyper-V, and two of those features require some virtual hardware, Automatic Virtual Machine Activation (AVMA) and Enhanced Session Mode.
AVMA lets Windows Server 2012 R2 guest OSs automatically activate when running on an activated Windows Server 2012 R2 Datacenter Hyper-V server, and Enhanced Session Mode allows a richer Virtual Machine Connection experience such as clipboard redirection by integrating with RDP stack in the guest.
OSs earlier than Windows Server 2012 R2 don't understand these features, which means they will see two pieces of unknown hardware, which the screen shot below shows.
On a Windows Server 2012 R2 guest OS, there are no unknown devices--they show under System devices as Microsoft Hyper-V Activation Component and Microsoft Hyper-V Remote Desktop Control Channel, per the screen shot below.