Can a lawyer do free work for a third party for referrals to him? 3rd party works for drug treatment center.?

Girl works for drug/alcohol treatment center, people ask for referrals for attorney, she refers one in particular and that attorney does pro bono work for her. Is this legal. It seems that there is a "captive audience" as these people in treatment need legal help.

: http://alcoholdrugstreatment.info/can-a-lawyer-do-free-work-for-a-third-party-for-referrals-to-him-3rd-party-works-for-drug-treatment-center