It doesn't get him out of any taxes. If you get examined by the IRS, they will do a deposits test off of your personal bank account and compare it to your tax return. If the deposits are higher than the income reported, adjusting for withholding etc, then they will go into detail and find out why its different. If you can't show proof its not income (gift from parents or loan or something else), it will be income.
Now if he said to pay him in cash, that would be a different story. I have clients from Mexico that will pay for my services in wads of cash and I'm pretty good about reporting it as income, I just don't have the best memory all the time, and some might fall through the cracks, on occasion, but not on purpose of course, because that would be illegal, and I'm not into illegal if my memory serves me correctly.