For my niece, if she was looking to be a working student, especially with the business mind my brother has, I know he will be looking at ROI and most working student positions I see posted would not pass his litmus test.
Which is perfectly rational for your brother. And if your niece is still a dependent in his household, then dad's opinion matters hugely. But your niece's calculus may not weight ROI nearly the same. And this is the whole point of the discussion as I see it--it is not for everyone, but if it fits the bill for more than one individual as an acceptable working/learning balance, then it is viable.