That is vastly different than becoming a Guardian. The Traveler uplifted many species (eliksni, ammonites etc.), only to abandon them when the darkness came. Only for humanity did the Traveler stand and fight and ultimately release its ghosts, very likely aware that humanity was a species that could wield its light and ultimately overcome the darkness. If other species also had this ability it is likely the Traveler would have made it's stand earlier. Just because an alien can be morally "good" doesn't mean its dead body can be reanimated by the light.