I see that the host OS of VirtualBox can be Windows Werver 2008, but it doesn't explicitly say 2008 R2. Can it equally run on Windows Server R2?
Also can the guest OS be Windows Server 2008 R2?
Virtualbox will certainly run on Windows Server 2008 R2. I have never found a Windows or Linux host on which VirtualBox did not run. The guest OS can also be Windows Server 2008 R2. I have one running right next to me.