pcb board to board connector dealing with ground current
If the concern is a ground loop, then the best thing would be to have a single point ground, with ground only on one connector, and parallel contacts/pins. Parallel pins will give the design a low resistance pathway for the large current. 

I've used 0.1" headers between boards and they worked good (but with not as much current and I used a single point ground, but had headers in many places on the board). I would also consider through hole and not SMT for the bottom connector as it would have more mechanical strength and avoid damage to pads. 

10A is a lot for a header, especially if it's a switching current. Let's say each header has 30mΩ (really depends on what connector you have, but probably is around 10-100mΩ) resistance through each contact. A 10A current would produce a 0.3V common mode voltage on ground if only one pin were used. Common mode voltage noise or offset on ground would be my biggest concern in this design.

Consider also that some manufacturers spec 3A for max current per pin on 0.1" headers.

If 6 pins were paralleled and used for ground, then the total resistance would be 5mΩ and only 50mV from a 10A current. I would probably use even more pins than 6 for 10A.