User blog comment:Jojo-a-gogo/Replacement Troupe members./@comment-1414102-20120727204353/@comment-5314364-20120728001612

But the whole point of Abengane is to restore Chrollo's nen. If he was a member he would not be able to do that. The judgement chain would kill Chrollo if he came in contact with a Troupe member. Thats why they need Hisoka to take Abengane to him.

In other words, he's just an associate to them. Though I'm not completely doubting the idea. He might be personally recruited by Chrollo after his mission is completed.