Not looking to play the "licensing police" - just trying to be helpful assuming the OP doesn't want to break the Windows license intentionally. My understanding of Windows licensing:
For the consumer versions of Windows 7 (other than the Family Pack), you can only install on a single machine at a time. The retail version of Windows allows you to uninstall/wipe clean and then reinstall on different hardware, while the OEM version is tied to the hardware it was originally installed on and cannot be used on different hardware, even if the old version is no longer being used (e.g., HP installations or home-built machines with OEM licenses).
Therefore, if you have a laptop or other PC with Windows 7, you can't use the same key in your VM on a Mac unless the version of Windows in question is a retail version (i.e., wasn't installed on the machine when you bought it, but rather was purchased later and installed by you) and you plan on discarding the old hardware. I'm in that situation and bought a new OEM license for use on my Macbook Pro.
As for the situation of creating a Bootcamp partition and then using the partition within a VM, I'm not a lawyer but think that's probably fine from a licensing perspective since it's not much different than accessing a machine remotely. It isn't a separate installation.
Note that the above limitations are largely licensing limitations and not technical ones.
Hopefully this helps.