A single person with $20,000 Annual Gross Income is contributing $600 per year to an employer-sponsored SIMPLE plan. He wants to open a Roth IRA. Must $600 be subtracted from the amount he can put into the Roth IRA? Or, can he contibute a max of $2,000 to the Roth in addition to the $600 into the employer-sponsored plan?

The SIMPLE will not preclude the Roth. You can do both.