Take a look at this tweet from April. This was only a few days before US law enforcement shut down BTC-E.
It is entirely possible that the law enforcement agencies of the US are already investigating Tether. Especially,
because they can always maintain that Tether can be used for money laundering.
I'm doubtful of a connection based just on this. The indictment was actually filed against BTC-e in January. They just unsealed it in July when they arrested Vinnik. So the timing of adding Tether capabilities doesn't seem important. I agree, law enforcement agencies are likely investigating Tether for a multitude of reasons.
I would be very cautios with the reincarnation WEX as well. It is possible that the US are using it as a kind
of "honeypot" to catch money launderers or hackers that sell their ransomware proceeds. After all
BTC-E used to be the main destination for these kind of clients.
When the relaunch was first discussed a few months ago, I had similar thoughts. However, I absolutely don't think that the US government would have refunded 55-60% of funds back to the users. I think that WEX = BTC-e and that Vinnik was just a patsy.