These are random spawns near the groupings of rocks and trees in between the Kylong Plains zone in and Sathir's Span. Most appear in the area where the tuskers, cats, stonepeeps, and Rilisians roam, to the right of the path going between the Kylong Plains sokokar post and Sathir's Span and just off the path between Sathir's Span and the Crystal Brutes. See the talk page for a list of random locations other players have found.
Only people on this quest can see these mobs. They despawn once hailed, but may respawn a short time later (that's random!) in the same location. They will show up on track. Keep circling the area and you should get all the mobs in short order.
Speaking with these spawns does not appear to break invisibility.
A discussion page exists which may contain more information