It's an interesting question though, as I would think that the use of Vantablack in the gallery itself would be a structural use, which limits Kapoor's rights. It's not being used in an artistic work directly, it's being used to highlight other artistic works. In fact, it would be about the only place Kapoor couldn't show any of his theoretical Vantablack work (to my knowledge, he has yet to exercise his Vantablack exclusivity rights). It wouldn't register as existing.