I just finished de'Arnise Keep. I still have some dog bones and the keep key. do they have any further use in the game. I don't even know what the dog bones were for.
There are no purposes to having them around. They were there to show that the dogs were eaten.
“The world breaks every one and afterward many are strong at the broken places. But those that will not break it kills. It kills the very good and the very gentle and the very brave impartially.”
You may want to hold on to the keep key. I went back to the keep once and all the doors/chests were locked! They aren't supposed to be but they were. If you plan on storing your stuff there I suggest you keep hold of it...