Fear is an instinct, there`s a reason that gants and such will lurk. His inclusion of tyranids is perfectly valid. They may not have individual souls, but even the Hive Mind Knows defeat and failure sometimes, so why not fear?
I`m loving this fluff mate.
I love the trinity of evil you`ve got in charge, and the fact that they are so callous, especially that succubus to her own wyches.
One thing though, Fenrisian wolves would become Grotesques, not wracks. A Grotesque is a tortured flesh sculpture, for lack of a better term, whilst a wrack is a willing Dark Eldar servant.
Think of wracks as nurses if the Haemonculus was a doctor.
They serve in the hopes of becoming a haemonculus themselves one day, or simply to stay in his good graces.