Or, stated differently, does a federal anti-discrimination law even cover a business that operates illegally under federal law?
Yes, it does.
In this recent decision, a Colorado federal court concluded that a female plaintiff who worked for a marijuana dispensary had successfully pled causes of action for sex discrimination and quid pro quo sexual harassment under Title VII of the Civil Rights Act of 1964.
Now, this does not mean that she will win. The court merely concluded that, on the face of her complaint, the plaintiff stated claims against the defendant. Specifically, she argued that she rebuffed two invitations for romantic dates from her manager and, shortly thereafter, she was fired.
So, whether you sell weed, widgets, or weed-widgets, if you have 15 or more employees in 20 or more weeks in the current or preceding calendar year, Title VII covers your business. And if Title VII covers your business, you need to provide anti-harassment education and training to your workforce.