The great Lost And Gone Forever Blog poses one of the the big questions from the recent episode quite well:
So it turns out that there really was a purge and Dharma was effectively wiped out, other than Ben. Also, while the Others seem to be semi-hippies, they're not above mass murder, which is nice. But this begs the question - why are the Others continuing to receive the Dharma food drops? How do the Others have such tremendous wealth and power to carry out their wacky schemes? The only thing I can think of is...-- "The Man Behind the Curtain" Instant Reactions!
His answer, which is what I've been thinking as well, is that the reason why there are still food drops, still communications and still recruits is that the hostiles took over DHARMA. Whether the hostiles are all natives or perhaps a combination of natives and DHARMA ex-pats becomes rather immaterial after the purge ... because then everyone is DHARMA. Having wiped out one side, they assume operations.
And perhaps even the goals of DHARMA. Remember, Ben insists they are the "good" guys. This also clears up some of the problems people have with a timeline where DHARMA references seem to persist post-purge.
The real wild card is Kelvin. We should be able to assume he was potentially the sole survivor of the purge, having been left safely at the Swan station. Others in hatches might have survived for some time as well. It's possible that the hostile's use of nerve gas might even explain the quarantine labels - though that seems like a stretch considering the fast acting nature of the gas. Unless confusion set in and some of the survivors were afraid the attack was in fact an illness.