Yip sums it up just don't quite fully understand the usd vs usdt.
the theory of usdt is that it's an altcoin backed by us dollars. that saves alt exchanges a whole bunch of legal head aches that they would have to address if they were dealing with dollars in bank accounts.
tether.to, the operation behind usdt says they have the dollars in their bank accounts and they only issue usdt if it has a real dollar to match it.
however you have to trust that the people backing usdt have the actual dollars. they've issued millions of them in the last few days and they're not a transparent operation.
they have banking problems so you can't withdraw the dollars to your own account and verification is pretty onerous.
https://tether.to/announcement/you might be fine. i'd prefer not to take that risk myself. stick with real dollars. it's just as seamless and an exchange that offers them will be more accountable.