Sure you can. If they are both 8 Ohms then, because you are using two of them, they'd each need to be plugged into the 4 Ohm outputs leaving the 8 Ohm output empty.
You could also run with two 8 Ohm cabinets to form a full stack if you want. The combo is identical to the head. It just happens to be encased in a cabinet with a speaker that you can choose to utilize or not.