Here are some of the features that are supported for virtualized environments.

• Presence
• IM (including remote access, federation, and Public IM Connectivity)
• Group Chat
• SQL Server back-end server

Check the full post over at OCSpedia.com http://www.ocspedia.com/Misc/OCS_Virtualization_Support.htm

Check out the supported server role collocation http://technet.microsoft.com/hi-in/library/dd425201(en-us,office.13).aspx