Validity refers to if a test measures what it is supposed to measure. Within the selection context this means: does the test measure a construct that offers a prediction on job performance? Of course every job or vacancy is different, but there is a body of research that reports on the predictive validity of the HEXACO personality questionnaire for different types of jobs or organizations.
When looking at the different factors of the HEXACO, the general conclusion is that the factor 'Conscientiousness' offers predictive validity on aspects that relate to overall job performance, leadership and undesirable work behavior. The factor 'Openness to experience' relates to creativity and adaptability within the organizational context. The factor 'Extraversion' predicts job performance related to social elements and general self esteem. The factor 'Agreeableness' relates to general well being within the job context and correlates with relationship building. The factor 'Emotionality' shows a relation with the ability of dealing with stress and the factor 'Honesty - Humility' a relates to counterproductive work behavior.