If it were the legal people uploading content to plant evidence, that's another matter, but I don't think have one department out of sorts with your legal position necessarily undermines the case (tenuous as it was to begin with).
By analogy, think of a software company which has one dept. that steals its tools, does that preclude the company from defending its own IP? Morally, maybe, but I don't think you waive your legal rights by breaking the law by default.
IANAL but I've never heard such of such a principle.