You're going to need one heck of a lot of Ballan Wrasse, to the point where there might a plague of them. Smacks of a very mucky industry's Green Cr@p PR smokescreen to me.
On rearing wrasse, another case for natural diet is preferred and best!
I read the original idea had been shelved because it was feared the salmon would eat their little helpers. Tolerated obviously for services rendered as is often the relationship between different species.