Running Microsoft Office Communications Server 2007 R2 in a Virtualized Topology
Today Microsoft released a whitepaper about running Office Communications server 2007 on virtual servers.
The main conclusion: Yes it is supported as long as there isn't any realtime component involved.
So IM, Presence on the Enterprise Front-end and the Access Edge server is supported, also the SQL Server based OCS Backend and the Groupchat server roles.
All other roles are not supported on Hyper-V.
You can download the whitepaper on the following location:
http://www.microsoft.com/downloads/details.aspx?FamilyID=0a45d921-3b48-44e4-b42b-19704a2b81b0&displaylang=en