Yes, it makes sense and it is legal. If he settles and they agree to forgive the remaining 1K, then they are supposed to report the 'forgiven' amount to the IRS. Anything 'forgiven' over $600 is reportable, by YOU, as income. HOWEVER, if you can prove that you were insolvent at the time the debt was 'forgiven', then you do NOT have to report the 1099 as income on your 2003 taxes. Insolvency's not that hard to prove if your liabilities are greater than your assets.
How old is this debt ? When was the original creditor last paid ?
IF he decides to settle, make sure you get the settlement agreement IN WRITING, I wouldn't pay them a dime w/o a signed agreement. You should also try to negotiate for either full deletion of any negative info they have reported on his credit report, or at least a 'paid' status. "settled for less than full balance' is a NEGATIVE mark and will not help his credit.