If the employee is responsible for paying the expense upfront and being reimbursed, no issue with using a gift card, certificate or voucher. The only issue that would come to play is if someone chose a more expensive alternative to utilize on of those methods vs a cheaper choice paid by CC. Personally, I have used Marriott gift cards, airline vouchers, whatever I have to pay for an expense I would have incurred anyway. No issue at all, ever with a submitted report.