Sure. The only requirement is that both uv maps use the same XYZ positions, which is the case in your above image.

The example is not good, though. Your texture uv map is missing the back and right side, and the lightmap contains gaps between the squares, thus using unnecessary extra vertices. If the lightmap does not contain more vertices than the texture, you can import it straight into the mesh. Otherwise you need to increase the vertex buffer by duplicating vertices, as in the the above case. You must then generate a new mesh that would be a little slower to render.

If you want to write a lightmap importer, you can contact me by email when you encounter a detail problem - for instance, how to replace the mesh of a model. I'll help you. It should not be very difficult.