That's not really true. Eldar who choose not t follow the path become outcasts and corsairs. They form their own pirate fleets and raid Imperial ships. It's kind of implied that they may work with Cabals on occasion, but they are not the same thing, they are two completely distinct groups.
I'm not sure what you mean here by shrugged off Slaanesh's corruption. Slaanesh never corrupted the Eldar race. The souls of the Dark Eldar are constantly being drained by Slaanesh, and in order to stave off being totally consumed, the DE devour the souls of captured slaves in order to restore their own essence. The Eldar wear spirit stones to protect them instead.I also am of the understanding that the Dark Eldar are fully aware of what they are doing and have shruged off slaanesh corruption. now that I think of it both Eldar factions have overcome the fall in oposite means and pity the other for thier apparent weakness.