I use server 2008 R2 SP1 with the latest beta ATI drivers.
Works fine.
I run mine in gui mode so I don't have to bother about using System account, so I've set it to auto login, with no lock time.
You may have to install the drivers manually, as by default catalyst didn't want to install openCL.  Just go find the MSI and run it.
I also use mine as a HyperV box, hence not running it as server 2012 as yet because, well basically, I don't need to as yet and can't be bothered.
If I add a second machine I'll put this one back as my standard desktop, dev and gaming machine, and I will run my miner on either server 2012 or server 2012 with no gui (datacentre).