Sometimes biographers do that yes. This one seems to be pretty even handed with the subject. Everything (and maybe more) that you wanted to know about Marcus Garvey.

As to the title. "A Negro with a Hat" refers to how W.E.B. Dubois (another prominent proponent of Black rights around the turn of the century) cynically referred
to Garvey. This referred to Garvey's sometime ostentatious display of fancy uniforms and plumed hats. At that time a number of organizations (Garvey's being only one) competed for Black membership in the U.S. and the world.