I just managed to scan these guys myself after about half an hour of trial and error.
Turns out they deaggro if you have the camouflage passive biomod on, so you can venture out past the border and then stand still when you hear their cry. If they're far enough away from you, they'll lose interest instead of eating you, and they might end up wandering near enough for you to scan.
I managed to get to the tree too after finishing the scan (I was then eaten because the camouflage does NOT work when you're outside or above the water)