Doing this actually occurred to me years ago. Sometimes you help a claimant get on benefits but you know from their medical records that they're getting better and have a realistic chance of returning to work. It doesn't happen much but it does happen. Since you already have their medical records, you're in a great place to spot these cases and to profit from providing "rehabilitation" to people who need little help anyway. I never did it because it seemed like a conflict of interest or at least it didn't seem to smell quite right. It's not illegal, though, as far as I know. Of course, I don’t know how Allsup is coming by its TTW cases.
I wonder if there are other affiliates of entities representing Social Security claimants on the TTW list, perhaps with names that can't be so easily connected.