Bodily Possession vs duplication by Sawyers Soft Side

Ok, whenever we have seen someone who is dead come "back to life" it has been in two different ways:
1) Their dead body has been re-animated (Sayid, Christian, maybe Claire)

2) A duplicate of their dead body has been made and is walking around like its alive (Locke, Ben's daughter, Eko's Brother...)

(Or when Hurley sees them, which I think is something completely different)

John Locke is the main evidence to this. We know that Locke is indeed dead, and that his dead body has been in a box for quite some time. But at the same time he has been walking around, and convincing Ben to kill Jacob.
We saw Locke pretty much turn into the smoke monster, kill a few guys, and change back.
Therefore, our old Smokey friend can shapeshift into whatever it wants. That would be the case with new Locke, Kate's Horse, Eko's brother, or whenever we saw Walt after he left the island. This, being as Jacob most likely wouldnt kill himself, has to be his nemisis in Black.

That leaves the other form of zombification, the direct reanimation that I assume is Jacobs doing.

Now we goet to the tricky part... Good vs. Evil

The whole time we have known Jacob, we have assumed he was the good guy, Im not so sure. Remember the red herring he caught when we first saw him and the MiB? If Jacob is indeed in Sayid, then Dogen referred to him as a "great evil that must be destroyed".


These are more my recent thoughts than a full and coherent theory, so help me expand, and tell me what you think.