I think the rename makes sense too, so +1 from me.
The only thing I want to ask: Is it conceivable that there may be some other functionality/context besides stereo rendering for which you would choose the QVTKOpenGLStereoWidget? If so, is there some other name that would be more fitting, something alluding to the way the widget is implemented maybe?
If it will only ever be a choice for stereo rendering, and only stereo rendering, then the name is good.