As in the majority of big bands past and present, hiring takes place by word of mouth, through personal recommendations. Sometimes musicians get a foot in the door by subbing on referral or by sitting in at rehearsals. He has autonomous decision-making power, determining who gets a job and whether or not they keep it. Marsalis grudgingly admits that sexism could hinder awareness of female talent. I heard about him as this boy in Houston.
Female musicians disagree.
Renee Rosnes, the Carnegie Hall Jazz Band's pianist, argues that the recommendation process affects women regardless of skill. I've had male friends tell me this and experienced it myself. Rosnes herself credits a longstanding connection for her entry at Carnegie Hall. He has always been a strong supporter of mine and I used to play in his small group. But asked for specific players, he comes up empty-handed.