Hi, Dan. It sounds to me like you are headed for trouble. Whether you use cement board and apply face brick or dig a shallow foundation and lay full brick, it eventually will move. When the cement board moves, the face brick will pop off. A shallow foundation will move, the concrete between the bricks will crack, and the walls will come down. Wish I could show you how much the concrete decorative wall in my back yard has moved. There is a root under it and it is 6-8" off level. And it started 8" deep. So whether from water or roots or something, your decorative walls will move and fail. Put in something like wood or lath that is made to withstand some movement.