I just installed the nimbus package on VL 6.0 Light.
Using the gtk theme switcher I can select the theme, and it shows icons and buttons as expected.
However, the window decorations (title bar with raise/minimize/close buttons) do not change at all; in fact, they stay the same (and rather ugly) whichever gtk theme I choose :-(
So I suspect this is actually not a problem with the nimbus package but a general issue...
What is missing for gtk themes to take control of window decorations?