I can't speak directly to civil3d but creating autocad objects for "internal" purposes happens often. For example, I create lines between 2d points just to get the angle, length, midpoint, etc. Just remember to dispose any autocad objects you create.
Since it would need to be loaded to be used, and needs a license to be loaded, and you have zero idea what kind of interdependancies are going to rear their ugly heads... just use Civil3D. Alternatively, you can code a simplified version using specifically what you need without being constrained by the Civil3D data types and work processes.
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