Each Detachment is applicable for traits. So, as long as each detachment shares the same keywords, each detachment will get it's own traits. So, you Could have a Blood Angels Battalion, and a Raven Guard Supreme Command, as long as each individual detachment has all the same faction keywords, they'd get the benefits those offer.
So, in your example, the Alaitoc Detachment would get the Alaitoc stuff (as long as all units in the detachment have that keyword), and then the Dark Eldar airwing will get the Dark Eldar command benefits (once they are able to have some).
Dark Lances are really good, so I'd try to get a bunch of razorwings with dark lances. Cheapish, super fast and very deadly.