I can't imagine that being inaccessible by X apps.. and I believe I've seen some apps report this info. It's something gdi32/user32 can then get for a particular screen/adapter by calling into winex11.drv (if not also something wined3d can use), instead of reporting "X Windows" for the card name.
I'm not sure, but I wouldn't expect these settings to be readable via some X11 API. There are X servers without an X config like that, e.g. the MacOS X server, or Windows X servers