I'm not a transient hydraulics expert but I would agree that these hammer loads "reverberate" through the system.
This link shows a good example:

https://www.youtube.com/watch?v=oZbguheiVs4&feature=related

You see two "positive" impulse loads followed by two negative impulse loads at the changes in direction. The elbow view in the video shows this the best.

If I was running a hammer load using a static equivalent, I would run it both positive and negative - if the system is nonlinear.