Could the "loophole" used by the Nemesis be his ability to use Locke's likeness despite the fact that his body was NOT used? Do we assume that every time a dead person is used it's via the "undead" theory, the person dies but since he/she is not buried can be used by the island gods to appear to others and cause some form of manipulation. Do we assume that they actually USE the bodies or only the likeness of the bodies?
If so, what is the big deal about Locke actually being dead. We knew he was killed when Ben strangled him so we must assume that the Nemesis was NOT using his body but only his likeness to convince Ben and others to follow him. So when we saw Locke's dead body why were we so amazed? It made me think that we have been fooled all along and that every time a dead person's likeness was used he still had a dead body somewhere. But we were led to believe that since Christian's body was gone that all those who were dead were also having their bodies used. But this doesn't explain Ana Lucia and Charlie. Ana Lucia was shot and killed in the hatch and her dead body lays in the hatch while her "likeness" appears to Eco. Also Charlie, his dead body floats around underground while his "likeness" appears to Hurley.
So my point is.... there is a difference between the "undead" like Christian and the use of a dead person's likeness. Perhaps this is the loophole, the Nemesis found a way to create a likeness without actually needing the body.