I don't know anything about anything, but I see Wikipedia says Tether is 65% "backed by commercial paper". Which as far as I can tell basically means IOUs, but IOUs that are considered somewhat legit. It definitely seems questionable, but I'm not really sure how to assess how bad it is or isn't.
1) https://en.wikipedia.org/wiki/Tether_(cryptocurrency)
Edit: I see elsewhere somebody saying "nobody in the commercial paper markets have heard of them"