This is my first post and I don't know if this has been discussed here before, so bear with me here.
I've heard a lot of people saying that Smokie is the same as Nemesis, but I don't think that this is true at all. The only correlation between the two that I can see is that they can both take on the form of dead people. We see Nemesis take on the form of Locke but as far as we know, and with the evidence provided, that's the only form he has taken that we've seen. Nemesis seems to do this for his own purpose, for his loophole, and doesn't follow the same actions and pattern that we see Smokie use. When we see confirmed uses of Smokie taking the form of the dead it's for the purpose of judging someone. We can see this very clearly in at least two instances, Yemi judging Mr. Eko and Alex judging Ben.
Another reason I feel that Smokie and Nemesis are two different entities is the fact that Smokie can be summoned by someone on the island. Now we don't know too much about Nemesis, but from what we've seen he doesn't look like the person that is going to come running to take orders just because someone was calling. I could be wrong on all of this, but rigth now there just isn't enough evidence to support that Smokie and Nemesis are one and the same.
Now my personal thoughts on Smokie is that he is a judge of sorts for the island. We see him referenced with Anubis, an ancient Egyptian god of the underworld. Anubis would judge on who would enter the underworld by weighing the person's heart against a feather to see if they were worthy of entering the underworld. The ancient Greeks would sometimes associate Anubis with Sirius and Cerberus, the later of course was the guardian of the Greek underworld. We also know that DHARMA would reference to Smokie as Cerberus.