True resurrection and the zombie

[FreeTheSlaves]

What happens if the BBEG kills the good duke, soul binds him, and some of his minions later animate the body into a zombie? Does the animate dead fail?
If not:
1) Why doesn't it fail?
2) Can the good adventurers true resurrect the duke (without destroying the new zombie first) if they acquire the gem in which the soul is bound?

My thoughts are that to true resurrect, the good adventurers need to peel away each obstacle. They have to make sure that the soul is free and they have to ensure that the person is not undead.

The question then is: is the undead zombie considered a creature in it's own right or is it still linked somehow to the former person that lived their life inhabiting their body. If that link is considered severed the true resurrection clause covering undead is null and void and the person can be raised. At this point we can theoretically have the living man meet a zombie that looks just like him, albeit with some wear and tear.