I did some tests as well, because I was curious.
It seems small (!) selfilluminating objects don't have any lighting effect on clouds, neither V2 nor V3. Neither raytracer nor path tracer.
However on surfaces you can get some result, but actually it doesn't look very good. If you use the path tracer the illumination of the environment by the selfilluminating sphere is incredibly noisy. And with the legacy renderer you'll have to use incredible high GI settings as Jordan already said, and it still looks bad and takes ages to finish the prepass. So, in your case using a lightsource would be the best way, I'd say.
But you can use huge selfilluminating objects (a large plane for example) to illuminate a scene. Or even the background shader. This also affects the clouds.
I hope, what I said is correct so far, but as I said, I did a few tests...