
Maurice S. answered 08/06/19
Qualified reading specialist with expertise in all aspects of reading.
In this sense, the verb "vet" means "to appraise, verify, or check for accuracy, authenticity, validity, etc." (https://www.dictionary.com/browse/vet).
When the author of the CMS wrote, "Vetted users create full projects..." they meant that in order to have the authority to make operational changes to a software system, users need to have passed some examination to determine their competence and trustworthiness. Users who have not yet passed this check can only create projects in a 'sandbox' which does not allow the project to affect the wider software environment, and only vetted and therefore trusted users are allowed to release projects from the 'sandbox' to the 'real' world where they can conceivably damage the operational software system.