We only have limited information on how cinematic rendering is implemented in various commercial software (only what we can deduce from demos, presentations, etc.) but probably they follow a similar approach (it is fairly trivial).
Note that if segmentation result is a set of non-overlapping segments then it is not always necessary to use multivolume rendering, but RGB color channels can be generated from the segmentation result, which can be combined with alpha channel can be computed using a scalar opacity transfer function:
Important update: volume colorization and SSAO prototype is now available in VTK + 3D Slicer and the results are very impressive. Quality is comparable to (and in some aspects better than) other “cinematic” medical image renderings and its computational cost is very low. See details in this topic: