It seems like the main attack scenario for this + legal AI would be during discovery: if opposing counsel gave you a poisoned PDF, and you threw it into one of these products to help you sift through it and got bad answers.

However, wouldnt this be a rather risky move? Courts authorized the discovery, so I imagine the judge might loose their marbles and throw the hammer at them if this came to light.

Yes, this particular vector is probably better in contracting than discovery. There is a duty of candor to the court and court rules that might come into play. In the case of contracting the attacker would be exposed to the jurisdiction's law of contracts. That might call it a "misrepresentation" or fraudulent thus making the contract void or voidable, but it's not clear "your honor I never read the contract but my LLM told me it was okay to sign" is a great argument either.