I've never heard of doing this, and it is a red flag of the customer having financial difficulty. If you do this a few times, and the customer takes the dive into Chapter 7, you've just donated a couple of loan payments to him.
On the other hand, maybe he intends to charge the loan payments, and pay the credit card balance right away so he can get whatever perks, (frequent flyer miles, etc.) that he can get by using the card. Really...No really...It could happen.