On https://www.hackerschool.com/faq they say
"International applicants
I'm not a US citizen. Can I do Hacker School?
Yes, assuming you can legally be in New York for the entirety of the batch (just under three months). We don't pay you, and we're not an official academic institution, so you shouldn't need a work or student visa. We've had people come from more than 25 countries to do Hacker School."