Affixing multiple OEM stickers to a single machine

So for any licensing question I would always recommend asking a Microsoft license specialist and to get it in writing (email, etc), as the licensing changes from version to version. Microsoft made major changes to how things are licensed between 2008 and 2012 versions of software (SQL, Windows Server, etc). Any company you buy the licenses from should have someone who is a microsoft licensing specialist.

From the licensing data sheet, your assumption would be correct. Two standard licenses should allow you to do (4) virtual machines. You would still only have one host of course.

http://download.microsoft.com/download/F/3/9/F39124F7-0177-463C-8A08-582463F96C9D/Windows_Server_2012_R2_Licensing_Datasheet.pdf

"Determining the number of licenses for Datacenter and Standard editions

Each license covers up to two physical processors on a single server. The minimum number of licenses required for each server is determined by the number of physical processors. For Standard edition you can add more virtual instances by assigning
additional licenses to the server (two incremental virtual instances are added per license)."

http://www.zdnet.com/microsoft-ups-price-on-windows-server-2012-r2-datacenter-by-28-percent-7000019168/

"Customers can also choose to assign multiple Standard Editions licenses to a single server, in order to increase VM density on that server"

As Cliff suggested, OEM licensing restricts you to that one physical host.

So if you ever want to add a second virtual host, you cannot fail over or migrate your current VMs without violating the OEM licensing. I always avoid OEM licensing in virtual setups.

I third Cliff's comments.  You can't use OEM to get the additional HyperV Guests

Official Microsoft document, look at Q14:

http://download.microsoft.com/download/4/D/B/4DB352D1-C610-466A-9AAF-EEF4F4CFFF27/WS2012_Licensing-Pricing_FAQ.pdf

This document states only license, not mentioning open volume licensing or OEM. (OEM is mentioned once in a non-related question). Therefore I can only conclude that any license, be it Volume or OEM, is meant with license.