Are Roth 401k contributions entered into TurboTax (as Roth IRA contributions are)?

No, all you need to do is enter your W-2. The Roth 401(k) contributions are listed in box 12 of your W-2.

1. Login to your TurboTax Account 
2. Click on "Search" on the top right and type “W-2” 
3. Click on “Jump to W-2”