Nepotism isn’t unethical. The owner of the company has every right to do what they want with their capital. There is nothing that says the owner must act in a rational or profit seeking way. A CEO must act in a profit seeking way, but that’s because he is accountable to the owner.
It’s also not necessarily bad business practice. You seem to be suffering under the misconception that the world is a meritocracy, and the ‘best’ person for a job should get it. That’s not how any of this works in the real world.
Regardless, you seem like a creative chap. You can come up with other examples of when a business owner might keep someone on payroll that wasn’t directly to extract value for the customer and instead to provide value for other reasons. I believe you can do it.
I can think up all sorts of things, but that doesn’t make those things good business practice.
What’s “good”? Maximized growth? Maximized returns? Having your face on the TV the most times you can? Making a name for yourself in your town? When you’re the owner, you choose what ‘good’ is because it’s your business.
And to my point, since the owner picks what is good, they will employ people whose output is valuable to the owner.
“good business practice” would be behaviors that are good for the long-term health of your business. These are objective, not subjective. You might want your face on the news but if it hurts, rather than helps, it’s poor business practice (just ask Papa John).