Butler skirts pretty close to nominalism, even idealism here, as she brings deconstruction into a more listenable mode. But suppose we give her the benefit of the doubt and think it through from the side of essences, yes, that dreaded term that Butler herself has done so much to expunge.
As I wrote in “Queer Ecology” (all right then, here it is...) this also applies to all life forms in general. It's called “satisficing” and it means that if you walk and quack like a duck, you are one. This must be rigorously distinguished from mere nominalism. What it really means is that lifeforms are strange all the way down (OOO-ese, “withdrawn”), even to themselves. And other entities for that matter. A rose is a rose is a rose, and no one, not even a rose, has a good idea of what that means. But for the proboscis of a bee, the rose is “sampled” as food. (See my previous.)