Yes, the hammer load can echo back and forth through the system. CAESAR II examples focus on CAESAR II modelling and data development and evaluating those "echos" do not add much to the data development (although those echos may add to the current response if the timing is right).
I see the hammer load as a pressure wave travelling through the system. This pressure wave pulls the pipe along its axis due to the differential pressure on upstream and downstream surfaces. The slug load is due to a change in momentum (same velocity with a different mass). This change in momentum pulls the pipe away from each elbow center, one at a time (although there may be interaction to the current response as mentioned above).