(an industry player could cause positive effects, like a huge purchase of Apple into a new industry like enterprise/government, or vendor neutrality for public sector purchases, or Microsoft committing to OSX as a tier-1 OS, etc., but a hedge fund can't do that)
Risk is their bread and butter. Difficulty - if it were easy, everyone would be doing it. Illegal - arguable but they're probably just good at not getting caught (and managing the risk of it). See eg. recent libor scandal.
I agree that this would be too difficult to pull off (one worker spilling the beans would be enough).
But "can make money on the market" mean "might make money" not "will make money". Worth keeping in mind that hedge don't just get stream of money from the market just for being hedge funds. You need to get good information somehow.
http://www.zerohedge.com/news/2012-09-30/presenting-worlds-b...
Second, it is very unlikely an external party can organize such action among a foreign insular and sequestered workforce without Foxconn finding out. They certainly have spies among the workers.
A hedge fund puts a couple billion dollar short on Apple, and then pays 20,000 Foxconn workers $5,000 each to take the month off from tomorrow and go somewhere else. That's a $100m outlay for a vastly higher profit.
It's not a serious suggestion but it's feasible. It's an interesting situation - an extremely highly valued company underpinned by extremely cheap labour.