As a cash basis taxpayer, you get to report income when it's received, so the entire amounts paid would be considered his income, regardless of the time it's specifically for. As an independent contractor, he should receive a form 1099-misc reporting his income for the year in box 7, by January 31st 2018.
Insurance sales positions are uniquely categorized as statutory employees and will receive a W-2, with the 'statutory employee' box checked. This is a rare categorization, but it's to your advantage because he would get the benefits of being an employee and be able to deduct his expenses on schedule C.
Either way, be sure to get a form from his company before filing because you want to make sure the correct amount is reported and that you report the same amount and in the same way that his business reports the pay.
