There's no harm in trying. Bitfinex are trying to show that they're doing all they can to get the users' money back.
Chances are slim, but it's better than doing nothing. The hacker surely can mix all that bitcoins eventually, but he'll have a hard time laundering the money. If the "bounty" is high enough and if Bitfinex agrees not to press any charges, the offer could be very attractive to the hacker.
From the article:
If the hacker chooses this communication route, the two parties can discuss within any one of the 2072 addresses currently holding the bitcoins in question.
Are these addresses publically known? Have the coins moved since the hack?