as you might have found out yourself, xv with composite effects enabled does work - sort of. The picture is a bit offset to the top drawing into the window title area.
Now, I have played around with raster - and did the following last night:
kwin --replace -graphicssystem opengl
and got a very pleasant surprise - the picture was not off anymore. Sadly, window resizing of the xv window results in a black window.
So it is a mixed bag.