When redeeming the gift voucher, the voucher is a payment method, just like other payment methods (cash, card, etc.). Therefore, the customer earns points on the purchased goods, regardless of the payment method. It is not possible to indicate per payment method whether points should be earned or not.
When redeeming the gift voucher, revenue is generated and loyalty points/amounts are given. This also prevents the possibility of double spending, namely when selling the gift voucher and again when redeeming it.