Hybrid renderers are a pretty common trick in the offline rendering world, or at least were at one point in time. I haven't kept up with RT tech for the past couple of years, but last I followed things, increases in CPU and GPU power were making hybrids less useful. We're basically at a point where first-hit fillrate (the main benefit of a hybrid renderer) is effectively useless in terms of improving overall performance, since all the interesting lighting effects and so on are the real bottlenecks.

That said, though, writing a hybrid renderer is still a fascinating and very educational exercise, especially if you're interested in learning more about RT tech in general.