University of Wellington (New Zealand) 'PredictIt', like the University of Iowa 'Iowa Electronic Markets', operates with the specific permission of the US federal regulatory agency (CFTC) that would otherwise regulate their tradable contracts. See for example:
> to operate a not-for-profit market for event contracts, and to offer event contracts to U.S. persons, without registration as a designated contract market, foreign board of trade, or swap execution facility, and without registration of its operators.
My understanding is that they don't need to register as an exchange because of this. That doesn't necessarily absolve them of being a form of gambling, does it?
You would have to ask a lawyer! I presume the adequately-funded academic research projects have, and are comfortable their contract-trading won't be prosecuted as "bets or wagers" under the Wire Act.
https://www.cftc.gov/PressRoom/PressReleases/pr7047-14