RenderSystem is the wrong place to do it. It's too low level.
See VctVoxelizer (Components/Hlms/Pbs/include/Vct/OgreVctVoxelizer.h) and see VctCascadedVoxelizer (Components/Hlms/Pbs/include/Vct/OgreVctCascadedVoxelizer.h) the latter which accepts static and dynamic objects to generate the GI.
Of course you'd need to add RenderSystem interfaces to perform the RayTracing API calls, but RayTracing itself should be encapsulated somewhere else.
The only thing I am wondering is that VctCascadedVoxelizer requires manually adding each Item to be tracked; while I am thinking that is perhaps a mistake; and GI per-object settings should live in Item; while VctCascadedVoxelizer gets attached to SceneManager to be the active GI.
But overall RayTracing should be encapsulated into its own interface that is plugged into SceneManager and makes the necessary RenderSystem calls.