Can Firm Culture Inadvertently Fail To Prevent If Not Actively Promote Unethical Conduct?

Yes.

See, for example, Eat What You Kill : The Fall of a Wall Street Lawyer by Milton Regan

A driven, talented and highly successful bankruptcy lawyer ends up in prison for making a false statement under oath in bankruptcy court. Big fees, a great deal of pressure within the firm, a bad decision that no one noticed (or did someone notice? should someone have noticed? it would have cost the firm a lot of money), did the lawyer believe that the statement he signed under oath was the truth or at least in the category of “no harm, no foul?”

In law firms perhaps no factor weighs more heavily than firm culture when it comes to ethical behavior. If firm leaders make clear by word and deed that ethics matter, other lawyers in the firm will follow suit. If firm leaders do not affirmatively set a high ethical standard, other lawyers in the firm will follow suit. This does not mean that law firm leaders are the proximate cause of either ethical or unethical conduct by other lawyers in the firm, but the example firm leaders set matters.