I did that once and it worked for me:
I had to restart and/or recreate a new panel, I think, not sure.
Note that some applications don't work the same way if they are in the notification area. For instance, when I use Variety Wallpaper Changer with the the indicator applet, I can change my wallpaper with the mouse wheel, which is not possible in the notification area.
I tried to keep the indicator applet empty by default but It seemed not possible to add it to the panel. So it's still there with just the nm-applet. It's OK that way for me.