Does the "No tax on tips" affect a Roth IRA Contribution?

I made a deal with my kids that I would match their earned income (up to the maximum) until they reach age 21 to put into a Roth IRA.   

 

I figured it would give them a good start when they get out of college.   One of my kids just finished his Freshman year of college, and his earnings are mostly tips working as a waiter in a restaurant.

 

Since those tips won't be taxed as income, will they be eligible to put into a Roth?

 

Thank you