User blog comment:- Darkchylde/Alluka as Nen exorcist/@comment-10528819-20150621222123

I can think in 3 explanations:

1.Hisoka don't know that Alluka can heal without any whiplash, and is not willing to possibly die before fighting.

2. Hisoka consider Illumi a great ally and can probably think on different ways to heal Chrollo without risking it's aliance.

3 (and most probal). Abengane healing already worked...