No, that's no good. What that does is it will wrap the navbar so if the window width is reduced anything on the right side will drop underneath, which is fine, but the menu items that drop underneath can't be clicked.
Try it out on my site yourself:
http://www.gamerperfection.com
Try it full window, then reduce the window so that the horizontal bar appears and you can see what I mean.
I assume the bar doesn't move with the horizontal scroll because the bar is in a fixed position.