He can do it. Doesn't matter whether he's a sole proprietor or a company.
You alrady know the main issue, which is whether he really is an indep contractor.
With a standard profit sharing he can easily get $40k+ into it. There might be an issue if he wants to get $15k+ in there as deferrals, too. I forget what the limits are (they seem to change every year

!!!), so my #s might be off.
He would be a candidate for a DB if he wants to generate significant benefits, too.