If you are a W-2 employee then your taxable compensation for Roth contribution cannot be more then the amount reported in box 1 on your W-2. Payroll deductions for employer plans are reported on the W-2 box 12 and are not part of box 1. So no, the income cannot be used twice.
**Disclaimer: This post is for discussion purposes only and is NOT tax advice. The author takes no responsibility for the accuracy of any information in this post.**
