Scouts are individuals that that collect information on landscape characteristics of a region, weather conditions, accessible pathways, near by towns or gather intelligence on enemy forces.
While Trackers focus on the habits, patterns, movements of animals and people in the wild. This is done through observation of foot/hoof imprints, markings of scent or claw marks, disrupted landscape and prediction of behavior.
Both these skills are used by Rangers to a degree. Most races and their military have a need for these professions and is common.