could they? do they have the technology? yes of course.
will they? are they? do they want to? is it considered a reasonable expense? highly doubt it.
i would not worry much about using a site like this, especially if you are being relatively anon about things. don't start giving out your real name, or address, or phone number, or primary email, or any combination of these things, and they would never have the suspicion of you being local to consider tracking the ip, if they even troll these threads at all. personally it think they probably do, but not for that purpose. its probably more about 'knowing the enemy", and getting more ideas on what stoners and growers do and the things they like/buy to aid them in their never ending profiling of the American nation.