I guess they could develop kemp anywhere, but this localized spot makes me think there was some injury to the skin on that spot and the new hair grew in differently.
For those not familiar with kemp, it is the coarse hair that is sprinkled thru the coat in varying amounts. It is usually more prominent on the back near the tail and on the tail.
I suspect some of Gracie's kemp spots are caused by flea spot treatment. Also, last year when she was in the throes of allergy trouble those spots developed at the site of some sores. In those cases they eventually grow out.