It appears that not all of the screensavers under KDE are "broken".
Try the "Solar Winds" screensaver under the Open GL group. If it works, try the following:
Change to root:
Make sure your locate file cache is up to date... speed it up with nice:
When it is all done, look for KDE only screensavers (*.kss files):
Now try each of these. I bet they all work. At least they did for me.
The problem seems to be those screensavers that are controlled by xscreensaver (the ones that work under gnome) and are probably linked to a problem with the xscreensaver.kss file (which I guess handles launching the xscreensavers under KDE).
Just some guessing, but I think it is going in the right direction.
Any chance that developers read these forums?