I have just completed a XenDesktop 5 project for 450 users whereby I needed to create a KMS infrastructure with VM's deployed via MCS in a Windows 2008R2 and Windows 7 environment. The Citrix official stance is that this is supported via a workaround. You need to create the KMS server, add Office 2010 KMS functionality and finally enable XenDesktop 5 MCS to deploy pooled images with unique CMID's that successfully authenticate with KMS.
The process is fairly simple but these are the basic steps that are needed:
Step 1: Create KMS Server
The first step is to enter your KMS key on your Windows 2008 R2 server you have chosen to host the KMS service.
2. Go to the licences tab and the MAK and MS keys assigned to your organization will be visible.
3. Copy the product key labelled Windows 2008R2 Std/Ent KMS B.
4. Go to Control Panel >System and change product key and enter the key.
5. If you already have an existing MAK key installed on the server you can replace the key. Open a command prompt and run > slmgr /ipk *Your KMS B key*
6. Run > slmgr /ato to activate the KMS server.
8. Create a KMS DNS service entry. Go to your DNS server and open DNS > Your domain > TCP and edit the _VMLS service property with your relevant server name.
9. Open the relevant firewall port on the server (1688) or allow the listed Key Management Services as a exception.
10. Check that the KMS server can publish its SRV records in your domain by running the following command > nslookup -type _vlmcs _tcp.
11. Check the KMS server has the correct key installed and is listening for a connection by running the following command > slmgr.vbs /dli*
Step 2: Create Office 2010 KMS Server
3. Check the Office 2010 KMS Key has been successfully installed on the KMS Server by opening a command prompt and navigating to c:\windows\system32 and running > cscript slmgr.vbs /dlv all.
4. All Office 2010 clients come installed with a generic KMS key. Test activation and run > cscript slmgr.vbs /dlv all. You will see the current count or Office KMS increment by 1. This is to be expected as the KMS server will not start activating until it has received 5 unique requests.
Step 3: Create XenDesktop MCS Gold image
3. Run ospprearm.exe in %installdir%\%Program Files%\Common Files\Microsoft Shared\OfficeSoftwareProtectionPlatform. This will rearm Office 2010.
4. Shut down the image and use MCS to create your XenDesktop pool.