If he is giving lessons for free, it should be no problem. If he is charging for them, then it is considered "commercial" and he would probably need a permit to do it on a public court. The pro can't tell him not to do it, but could report it if he is charging for the lessons.
I give my own kids lessons on public courts with baskets, props, targets, etc along with other kids sometimes. I don't charge for it, though, I just like my kids to have the company and training partners.
"More Sureshs, less Maxima for a better TT." - Power Player