Seems not right to have current air drivers and current drivers delivering ground making less. Kind of like the show up to work bonus. Non union, seasonal employees making more than union employees.
The union (local or otherwise) had to OK this arrangement in order to not disturb the retiree's pension. In other words, it has to be agreed to.
And, as for the company, it's a winner. No training other than any new technology is needed. Some retirees do it for the money, others just out of boredom.
What's the problem?