Yes, that's what I mean when I said, "The issue is not necessarily about whether the relationship itself is ethical, but how it appears to observers and if it affects the organization."

If you need to get Bob's manager, Carol, involved to manage Alice when things go poorly, it means that you should have had Carol managing Alice from the beginning. This is the only way I've ever seen it work well. Alice is under Bob in the org chart but all of her performance reviews are done by Carol, and Carol signs Alice's pay sheets, et cetera. I've seen this particular case happen a few times where Alice is Bob's daughter or where Alice and Bob were married before they came to the organization.

This is not possible when Bob is the CEO.