Yup, then your Win VM will also be set to use 1680x1050 -- same "virtual resolution" as the Retina display is using.
I'll also check one of my colleagues' Parallels machine to get a better sense of what you're talking about, most of us are using Fusion, but a few are using Parallels. In my case I'm using Outlook, Lync, Word, IE and a few other apps in the Win8 VM. Win8 responds very nicely to changes in display resolutions (going from full screen to windowed, for example) and is very VM friendly (recognizes that it is running in a VM and does not impact battery life or CPU cycles substantially).