tldr: I didn't use Flightaware; I observed these aircraft directly using my own receiver, decoding their callsigns and squawk codes, and correlated with FAA records and the company confirmed by the FBI itself to be a front.

But it's true, most of this evidence is still circumstantial. Just because a company with an odd name and no internet presence has the same PO Box as the DOJ doesn't prove it's a front company; but it's pretty suggestive.