I'm not sure whether Stirner actually had a say about chaos being essential to anarchism, though we can say that it can be implied from his writings.
And, no. When post-left anarchists talk about "chaos" they don't take it as a means for anarchism. Quite the contrary, seems Hakim disapproved of "revolution" and supported instead "poetic terrorism", or some underground samizdat that will support anarchism through art.
When post-left anarchists stress "chaos", they mean the lack of any human essence and morality that ought to guide us. They start with the existentialist tenet: "existence precedes essence". And so we are "doomed to be free", hence, without morality/essence, we are chaotic. So, I guess, we can say that Stirner somehow sympathized with this thought. He even discussed about "insurrection" of one's being.