Matthias Elter wrote to the KDE core devel mailing list about his progress in getting KDE to play nice with Window Maker and Afterstep "applets", and included some eyecandy to boot. His message follows below.
I have hacked a kicker extension that detects and embeds dock apps. Dock apps like Window Maker or Afterstep "applets" set a standard XWMHints hint (IconWindowHint) which is recognized by the extension. Save and restore is not implemented yet and the layouting is not perfect. I will fix both soon.
Eye candy: http://master.kde.org/~me/dockbar.jpg