Yes, you can count his premiums on your tax return.
For purposes of the Medical Expense deduction, a 'medical dependent' can have over $4050 of income, if all other tests for dependency are met (such as providing over 50% of support).
However, only the amount of medical expenses that are over 10% of your income (7.5% if age 65 or older) will be actually used as a deduction, and if you don't already Itemize your deductions on Schedule A, the deduction will further be reduced or eliminated.
