Well, i personally don't think that "Smokey" is any form of shape shifter. I know i tend to disagree with many opinions people give concerning this show...guess its just what i do...like to offer other views to largely accepted theories/ideas.

COULD Smokey be some sort of shape shifter? Yes

However, i think there is something far greater happening than Smokey just taking the shape of other people. One of the largest LOST mysteries which i am still wondering about (but which others have seemed to completley forget about) is the whispers and voices people heard in the jungle during season 1. I can't remember exact episode numbers, but i know more than one person experienced these. Ever since season one, my theory has been that there are the "Others" and there is Dharma...two seperate groups. (i forget his name) But when Desmond first got into the hatch, his partner told him to be careful of the "hostiles". I don't think he was refering to Dharma in this case. I think he was refering to whatever made the whispers, and possible made things appear (other figures of people maybe?)

I'm getting way into theory here, so i'll slow down. All i'm saying is i can't accept that Smokey has taken on these shapes quite yet. I think there is not enough evidence to support such a claim. It would prove an interesting addition to the show, but i'm still hesitant.