I'm not sure I saw that thread, but usually if a conviction is "set aside" it means that there was some procedural or legal defect in the undelying proceedings and the conviction is vacated to allow for new proceedings possibly including a new trial. That is very different from expungement or sealing where the undelying conviction is not disturbed. Whether an expunged conviction needs to be disclosed depends on who's asking and what they are asking. Illinois doesn't set aside convictions unless they were obtained in violation of the law or for innocence.
Not everywhere. Convictions can be set aside if they have been taken under advisement and the offender has gotten in trouble during the probationary period. That is how a plea under Michigan's Holmes Youthful Trainee Act works. Nebraska also "sets aside" convictions based on rehabilitation:
http://court.nol.org/self-help/set-a...m-convict.html
Also look at my State's Court of Appeal's ruling in Carr v Midland County:
http://scholar.google.com/scholar_ca...en&as_sdt=4,23
An expunged conviction (using my state's definition of the term) is vacated. Our Attorney General used this distinction to opine that an individual with an expunged conviction was "not convicted" within the meaning of our CPL law. Based on this, the Attorney General opined that the individual was not "convicted" of a disqualified conviction.
http://www.ag.state.mi.us/opinion/da...0s/op10208.htm
The feds are going to look beyond the exact mechanism involved or label involved to see whether the ruling was based on a determination of innocence, procedural irregularities in the original proceeding, or simply rehabilitation. If the determination was based on rehabilitation, they are not going to honor it (unless it is governor's or president's pardon) regardless of the exact legal mechanism that a given state uses.
This is an area of the law where every state is different and the same word is defined differently once you cross a state line. The bottom line, however, is that the feds are a separate sovereign and are not required to respect state law on the subject.