Gateway Health has been dipping a toe into Medicare’s special needs programs with encouraging results at a time when enrollment in the company’s bread and butter Medicaid program has flattened. Gateway offers Medicare plans for people who are eligible for both Medicaid and Medicare, a group that is poorer and sicker than people with either coverage alone, and also Medicare recipients who have heart disease or diabetes. Gateway has more than 43,000 members in these special needs plans, a total…