The site descibes serveral topics about the OCS 2007 R2 version:
Installing and Managing Office Communications Server (Communications Server) 2007 R2
Deploying and Configuring Communications Server 2007 R2 Clients
Monitoring and Maintaining Communications Server 2007 R2
UPDATE (feb. 14.)
I passed this a few days ago, and the exam is mostly OCS 2007 R2. The only relations to OCS 2007 (and LCS 2005) is 4 to 5 questions about upgrade scenarios.
For those planning to take this exam be sure to know your R2 features, Phone number normalization, Address Book Service, TCP & UDP ports and archiving role.