Regarding referral fee arbitrage... An organization might want to stop that on ethics grounds: if the employee is making money by redirecting a referral through a recruiter, without disclosing that to the organization... then the employee might have two conflicts of interest:
* employee is disregarding an official process, to enrich themselves at a cost to the organization
* employee might be involved, officially or unofficially in deciding acceptance of the candidate, without the organization having an opportunity to manage that
Besides the immediate impact of each incident, this can lead to a culture in which such things are viewed as OK, which can then escalate to much worse incidents/scandals, bad morale, dysfunction.