Yep. .cgr files are simply a tessellated version of the CATIA solid. It only contains a simplified version of the outside of the solid. The Tessellation process consists of putting little triangles all over the surface of the solid. The number and size of the triangles is determined at generation time by a "sag" value. This "sag" value tells CATIA how far from the actual surface the triangles can deviate.
The best you could ever hope to get out of a CGR would be the definition of those triangular facets, and that would not be nearly accurate enough for anything except visualization (or sometimes for Interference Analysis).