As Tangerine said, make sure he doesn't get stuck with a bunch of worthless pesos.
The problem is not bringing dollars in, but buying dollars to get rid of any unspent pesos on exit. He should only change enough pesos for what he needs - not all at once with the thought of changing them back to dollars on leaving.
Most likely, he will not be able to buy a single dollar legally when he returns, no matter what the law says, or AFIP says, etc, unless he finds an expat or local willing to buy his pesos (not farfetched - I've bought pesos from family members who are trying to save in dollars and I have my monthly expenses).
