Going along with the mechanic idea, perhaps a maintenance worker, whose job it is to fix the infrastructure of this network when part of it gets corrupted. they could also be people who reinforce their shelters/buildings from radiation. can this radiation be part of the reason why these places are corrupted? if so, they'd be in effect protecting information.
hmm, or to think the opposite of this, a wrecker. are there places that are particularly harmful that the government would want people to keep out, so that they would resort to destroying these places?
if these corrupted places are physically destroyed, the information there would be lost or inaccessible. which leads to someone from the underground whose job it is to retrieve bits and pieces of information. For some reason, I think of dumpster diving, but I think that's too obvious..it's not exactly a job either, but someone in the corrupted zone has to be desperate enough to do it.
Hmm, and now it brings up questions in my mind about waste disposal or the impact of pollution of this time period. Would a normal every day street be polluted in the real world?