i think the so called honour is pretty much hunting regulations that was enforced by law and to maintain a healthy prey population.
As for concept of honour for predator, it will be more of an individual thing. Being sentient creatures with personality and tech, predator had individuality as well. Besides imo its much more interesting then seeing them boardly classified as A "honourable space samurai or B "Sadistic space redneck".
The pred in predator 1 shoot up poncho because despite being wounded, poncho was still a combatant and therefore a piece of fine trophy on the wall. Its not like he only had 1 seconds worth of memory.