very interesting ideas, michel ...
I would only point out that the Others weren't safe from Smokey. They had the fence around their whole compound to keep it out. They may have taken precautions when out and about.So the Others who lived in Otherton were not immune. Certain people may be immune, but not the whole group.
Interesting that in 1977 there doesn't seem to be a smoke monster problem. No fence. Instead it is the hostiles that are the concern, Richard's people. There is a smoke monster when Danielle's people land in 1988. So did the smoke monster exist pre-incident? Did the sickness start after the incident?
By incident I mean the energy released at the Swan in the original timeline, not the bomb detonation.