There are a few problems when trying to get special characters into wrack units. It really is one of the biggest efficiency problems the wracks have.
A razorback for instance is set up perfectly for a 10 man tactical squad to combat squad with just enough room for the independent character. Wracks on the other hand, can only get a special weapon every 5 wracks. If you only want 5 wracks for a venom transport, that precludes any special character. The same goes for a raider with 10 wracks with 2 special weapons.
I am not a fan of the Hexrifle personally, and giving an acolyte a special weapon does not grant an extra attack. This limits an acolyte in my book to a +1 leadership for the unit.
With these limitations in mind, (my mind), I have been using 5 man wrack units with a raider transport. I have seen marginal success this way, however, I did discover a very excellent tactic for using my wracks on the tabletop.
Wracks in 10 man units are extremely durable. Unlike Warriors or Wyches that tend to lose every wounded model when the raider goes up in smoke, Wracks are extremely durable enough to remain in raiders while in play. Not to mention that with dual liquifiers you can flame from any point of the hull on the raider as long as you do not move over 6". Also wracks in cover recieve a 4+cover save and then their feel no pain.
Dark Eldar can throw down a lot of anti-tank fire, and having a couple raiders filled with wracks in your troop choices with dual liquifiers is an excellent tool. Remember that wracks do not come with grenades. Wracks deal with units in cover with liquifiers, and ones not in cover with assault. (technically both, but efficiency means you do not want to assault into cover unless you have to or overwhelming odds.)
Round 1. Move in 12" and fire off your lance, or go flat out to get into the enemy or its flank close to a targeted transport.
Round 2. Move 6" double flame away from any point of the raiders hull
The primary points: Wracks can stay in their transports, and dual liquifiers from any point on the hull are nice. Not to mention you are moving objective claiming units forward to claim objectives later. Wracks in cover can be hard to remove, and in general Independent characters should probably be travelling with someone else.