At least two of these dervishes spawn on the island with the dock. One spawns at about +5700, +1000, +170 near the three static cougars beneath a tree and begins roaming the southern hilltop. Another one is a static spawn just south of the gnome pirate igloos at about +4375, +1500, +100. The respawn time seems fairly quick, maybe 3.5 minutes or so.