I dont believe you can do this at all. I am assuming you meant installing Windows Server R2 as a Virtual Machine on Proxmox. A Virtual Machine does not have direct access to Host Hardware. It only sees the software layer that binds the physical hardware and virtual environment together. There are ways where you can provide direct access so some devices such as Video, Sound using pci-pass through. But i dont think you can handle physical RAID card from a VM. Since you already installed Proxmox on the RAID, Proxmox itself using all aspects of the RAID at this moment.