In Doe v Connecticut the registrant brought suit on behalf of himself and similarly situated offenders on due process cause. SCOTUS took the case meaning a legit (group) claim(s) are possible at least on process attack.
The registrant had entered into a plea bargain thereby also entering waiver for appeal. HE LOST 9-0. In other words do not go complaining about process when you agreed NOT TO! Intelligently and voluntary!
However some did not waive, they are those whom opted for bench trial. They also may be actually Innocent. Innocent people rarely plead guilty to what they did not do. See Barry Sheck I have.
Justice Souter mentioned those especially in his answer. Innocents also pose no danger yet registration applied. Also terms applied without opportunity to mitigate\ defend via council http://www.law.cornell.edu.
SCOTUS also addressed ( redeprivation hearings) in this case deeming no Constitutional right exists.