I have never had a home insurance where at least the insurance broker didn't come out and do an inspection. If there are major issues, siding missing, or broken steps, they will add exclusions to your policy. If the policy does not specifically state an exclusion for the deck, regardless of the previous owner's contractor issues, I would think this should be covered. I would argue it with them at least.
Now I've only owned in Wisconsin and Michigan, and laws could be different in GA but I doubt they'd be that different. Check with your Insurance Commission and their website - it looks like there might be some possible info there.
GADOI Home Page
If it comes down to it you could go after the home inspector that you had when you purchased the home (I'm assuming you are the owner.) You could go after the previous home owner... OR you could go after the city/township for allowing the deck to be built without a permit and inspection. This is NOT something that would normally be allowed to be built without permits and inspections in any area that I have ever seen. All said and done though - technically, the INSURANCE company is supposed to go after those people - that's why we have insurance.