Negotiators for Jackson Health System and SEIU Local 1991 agreed Tuesday to a contract that calls for $52 million in concessions for each of the next three years, but workers could get some of that money back if they find ways of saving the hospitals money or gaining new revenue. The tentative agreement will be voted on next week by the bargaining units covering nurses and other healthcare professionals. A third unit, covering physicians, was still in discussions with management late Tuesday afternoon.