Windows Server 2008 R2 is not listed as a supported environment because Microsoft has already EOL'ed this version, but I think it should work fine as long as you are using IIS Web server with .NET Framework 4.x.
Just keep in mind since it is an unsupported environment, we would not fix any bugs that cannot be reproduced on the newer versions of Windows Server.
Best regards, Armeen
Ok, thanks Armeen. This is just an interim solution until a new server is built.