No. Windows only uses the area you define the working window as. Remember you have three modes:
1) Coherence. No window, just Windows applications working in the Mac display.
2) Full screen mode. Here there is a 'window' occupying the full area of a screen and Windows works inside this.
3) Windowed mode. In this you define a window (box stretched out to the size you want), and 'Windows' runs inside this box.
If you stretch such a window out to fill the 'full screen', this behaves very like full screen mode, except:
a) You still get a bar at the top, giving the connection details etc..
b) You are running vectored through the Mac screen drivers, not directly through the 'full screen' drivers, that PD11 had.
It is these full screen drivers that have problems in multi-monitor mode.
Obviously there is a performance cost to vectoring through the Mac drivers, but I've found the performance to still be very good, and the loss of a thin bar for the connection details, status etc., at the top of the screen, is minor. Anyone wanting to run games (which is where full screen did offer advantages), can't go this way, but for 90% of users who want a Windows screen a Mac screen (and possibly some others), this does work.