The early Parallels beta that I have installed could not boot a real partition on the hard drive. This means that the same copy of Windows was not available to both Boot Camp and Parallels, so you would be looking at two seperate installations. I don't know whether this has changed in the latest version, but there are no clues on the Parallels website.

How this would work in terms of licensing I am not sure since they are actually on the same computer.

It wouldn't be convenient having to look after two seperate instances of Windows for sure.