OEM and Retail are the same from an OS & installation point of view, it's only the licensing and packaging that are different.
If you install Windows to a Boot Camp partition, Parallels (or VMWare Fusion) can create a VM using the existing BC installation and activation.
VMWare has historically been a little less troublesome than Parallels from an activation viewpoint (my own experience with Fusion was seamless and transparent), but my understanding is that Parallels is better about it now. I'm sure there are others that can chime in on that.