Kiki...alien the whole time?
I'm thinking that Kiki was definitely an alien the whole time, but then again there is a slight possibility that he wasn't. The one thing that stands out in my mind is the scene where the Gardener breaks into Zane's house and drops the orb in it, and Kiki comes over and looks rather perplexed and concerned. Maybe he wasn't in the loop? Maybe he didn't know they were trying to eliminate Zane? Or maybe he was human?
The only thing that could be possible is that they Gardener was suspicious of Kiki after encountering him, so maybe they got rid of him, and replaced him with an alien that used his skin form.
Just one of those great mysteries in the movie that gets you thinking.