> is it impossible to secretly employ a lawyer to own a firm for you?
Yeah, even that would be against the rules of ethics. The rationale behind the rule against non-lawyers owning an interest in law firms is that a non-lawyer should never be in a position to dictate or influence the legal judgment of a lawyer. So if a non-lawyer is directing a lawyer's work (in terms of "legal strategy", basically) that's unethical. Of course, a client can still direct a lawyer to file a legit suit or to take a settlement offer or something like that.
As for the tech company example - this would probably be okay. As long as your advice isn't really putting the company at any disadvantage at all, it's probably not unethical. If you're benefiting on the side from the advice you're giving your client somehow, though, that might be breaking the rules of ethics (there's some stuff in there against insider trading, etc.)