It is possible to deploy a resource forest using Exchange and Lync in their Online version. For a similar scenario, there is a Forefront Identity Manager Connector for Windows Azure Active Directory (http://www.microsoft.com/en-us/download/details.aspx?id=41166). However, in the past few months, Microsoft has published a new tool, Azure Active Directory Synchronization Services (AAD Sync). Quoting the MSDN site http://msdn.microsoft.com/en-us/library/azure/dn790204.aspx, this new synchronization service allows the user to:

Right now, this tool is in the general availability stage. In the How it works... section of this recipe, we will talk about the AAD Sync working logic. Now, we will see how to deploy it.