It is almost certainly easier (in practice) to perform an edge detection or similar post processing step (usually on depth and/or normal map) in image space to get something that looks like the occluding contour. The utility of that data is limited, however.

At the risk of getting semantic, I'd argue that the raster representation of such a contour is not the contour. That is, calculating the contour as a raster image is just calculating something different.