As a lvl 70 THF I must've killed every Gallnipper around the perimiter 4 times over and never got the ginseng. I finally decided to try the Ogrefly in J-9 & K-9 and got it on my second kill. I hope this saves others some time.
On the East side where the low level mobs are. Just keep heading east through the tunnels and you'll see them as soon as you get to the main open area.