Our business has a significant amount of cc spend because of ad networks that don't charge processing fees, and high CC limits acting as nearly free lines-of-credit. This generates something like ~$100k annually in points value for us.
We got some opinions from a few tax attorneys and CPAs a while back on how to handle this, and the consensus was clear that as long as points stay in the programs and are redeemed for flights/hotels/etc, they won't need to be recorded as rebate to expenses or as income.
Applying the rewards against your balance should be recorded as rebate against expenses rather than income. Also, worth noting that some cash back programs have started issuing 1099s, depending if it's a "Bonus" or percent of spend.