It's hard to do that, considering that Bitcoin is anonymous. And I think that they won't use that kind of public service, they will probably make their own mixer and use it by their own.
Bitcoin is
not anonymous. It's pseudonymous. While an address is not by definition linked to a human identity, it certainly
can be in many ways if a user is not very careful to cover all tracks.
Making your own mixer with that amount of hot coins would just put a target on your back when everyone realizes that you're delivering tainted coins from the Bitfinex heist to your customers.