There`s a difference between getting someone to engineer, or assist production, and just downright do it all for you.
The problem lies also with the person doing the engineering.
If you have a huge hand in what goes on then you should get co producer creit, and it`s your responsibility to get it.
If your sitting there doing everything and all the other guy is doing is going "yeah, I like that" then you are being the creative part of the deal.

Ghost writers suck. How anyone can have the Ego to claim the creativity of someone elses work is beyond me. It`s dishonest and I question these individuals whole motivation.