In this case the Lighting value is added to the already existing Emission values. I think it makes perfect sense, because it is converting the previously reflecting particles into self-illuminated particles that produce the exact same scene if rendered without the original lights. Absorption doesn’t affect the light scattering on a particle or how it is emitted, only how light is attenuated as it travels through volume-filled space.
What exactly would a “Shading” channel do?
You don’t need a light for Emission only, it uses Camera aligned planes when doing the Light independent pass.