The hacker would likely sell it outside of exchanges directly to others in chunks.
That would be safer and wouldn't shock the price unless the buyer buys a significant amount and dumps.
Lets say some of the "stolen" coins get moved to Poloniex. Poloniex is registered in the US isn't it?
I could see some kind of legal action arising.
He could tumble it (mix it with "legit" ETC coins so much that it's hard to track which coins are from the hack).
Or use other exchanges.
Or there's the argument (however silly it might be) that the hacker not being a criminal because het used what the code allowed.
I also don't think Polo would do anything or would be forced to do anything with the tainted funds.