How lenient are background check agencies on unpaid internships?

I did an unpaid internship for my dad's business about 3 years ago. I am being background checked right now and they asked for the W2/paycheck stub for this internship. I am inclined to tell them it was for my dad's business and unpaid, but just the fact that unpaid internships are "technically" illegal here makes me a little worried. Are background check agencies usually lenient on this sort of things?