No, they don't get a bonus based on discount policy. It's in the handbook. It's something TMs agree to when they start. The point of it is to limit interchange fees, which aren't much each time; but, multiply that fee by every tm transaction across the entire company and those fees are up. This is why you can only use your discount with cash, check, target cards, and gift cards. Using a non target card to buy a giftcard and then using your discount with the giftcard is circumventing the policy so you can essentially use your tm discount with your regular debit/credit. Target is still paying interchange fees. It all has to do with Target saving money. You're free to think it's a stupid policy, but it's one you agreed to wha n you started working and the handbook clearly states that there may be corrective action for abusing the discount policy up to and including termination.
Honestly any tm who has a checking account without bad check writing history at target, spends money at target, and doesn't have a redcard debit...they're just losing money.