As promised, Microsoft has released supportability statements for various Communications Server versions when used with Server 2008 R2 hosts and domains. Yesterday two TechNet articles were released to address both scenarios.
Server 2008 R2 Domains
Previously no version of Communications Server was supported when deployed in an Active Directory environment using either forest/domain functional levels of Windows Server 2008 R2. Upgrading to or installing Windows Server 2008 R2 domain controllers would also cause problems with an existing LCS/OCS installation, preventing the later deploying of additional servers/pools.
With the release of the Knowledge Base Article 982020 there is now a documented and supported resolution for supporting Server 2008 R2 domains. Basically the ForestPrep deployment step must be reapplied in order to replace configuration information in Active Directory that was erroneously removed by the upgrade of AD to Server 2008 R2.
Server 2008 R2 Hosts
More importantly OCS has not functioned correctly, nor was supported, when installed on a Server 2008 R2 host. Various SSL-related changes in Server 2008 R2 prevented some conferencing features from working due to certificate errors.
But now Knowledge Base Article 982021 details a supported resolution in the form of installing a number of Windows Server and OCS patches, as well as changing some default security settings in the host OS.