Why don't you try it out? I remember writing chemistry programs that have had buttons on the right side of the screen that showed up even though OpenGL was actually being rendered to the entire background, and I don't believe I did anything special for it. I believe we have given you the answer already, and that is you simply need to call glViewport when setting up OpenGL with dimensions smaller than the size of the Win32 window you are drawing on. This will limit anything OpenGL wants to do to that portion of the screen.
I've already got menus, however I think if i put any controls, they will just be hidden due to OpenGLs background clearscreen color.