According to the article cleaner fish (they eat lice) are being used.  But it does not solve the escapement issue.  Also since sea lice really thrive because there is so much available food in the pens farmers would probably have to have at least as many cleaners as salmon.  It's probably cheaper to buy the chemicals they are also using.  If the absolutely must farm salmon it should be done in closed pens with no possibility of escapement and interaction with wild fish.