sorry to butt in, but i have some ideas (some of which belong to other people) that kind of deal with this.
one thing that points to the woodsman existing before the bomb is the fact that time (as it regards the lodge and it's inhabitants) doesn't seem to move in a linear, forward progressing fashion.
this seems to hold true to a lesser extent with those who come into contact with the lodge.
for example, laura wrote about annie in her diary. in the original series, laura never met annie. she was dead long before annie got to town.
as for the lodge and it's constuction, the greater mythology of the show points to the lodge having been the subject of native american myth going back for centuries before the town of twin peaks ever existed. (check out mark frost's recently released book)
i also read somewhere else that the woodsmen could be the dead spirits of the woodsmen who died in the fire that killed the log lady's husband. this of course only holds up if, as i just mentioned, time as it pertains to the lodge doesn't move forward as the log lady's husband would have died well after the bomb.