As a conservation officer, I can tell you that if video evidence exists of a person digging up ginseng on a certain property, then ginseng they are found with will be charged to that particular case. It is now a Federal crime.
That is how I would prosecute the matter, and I am very interested in this, because someone has been poaching ginseng in my jurisdiction, and we are planning on setting out trail cams to catch them in the act.
Analyzing soil samples can be done, but it's like asking for DNA analysis on that cheeseburger that you swore the burger boy spit in. It's up to you to spend the cash for the test. Do you have 5 grand to throw out for the testing?