The USTR is essentially an official corporate proxy and having government officials act as a go-between, asking corporate representatives what they want and then trying to get it for them is an insignificant technicality -- if a crime is contracted out, you don't spend time making a real distinction between the criminal who actually carries it out and the criminal who commissions and pays for it -- the distinction technically exists but really it's meaningless and discussing it actually distracts from the facts of the case.

They're in the luxury hotel so the round-trip time between the negotiating table and the corporate representative's hotel room is minimized -- they can all be in the same hotel. Government employees don't live in the lap of luxury by any means regularly they are generally poorly paid (that's why they swap between corporate rep and regulator, the regulator role doesn't pay well), it's the proximity to corporate wealth/corruption that's incidentally getting them nice accommodations.