The Title pretty much asks the question - baking a texture that has a normal texture attached also bake the normal map to the texture atlas?
No, the textures atlas is just that, for object textures only, and is adjusted with the tabs below the bake tab..so that you can include or exclude texture properties from the texture atlas. l think that the process could be applied to the normal maps too.. but the manual is not clear on that.. so proceed with caution...
If you use the textools addon https://blender-addons.org/textools-addon/
then you can bake the normal easily