I consider Nox a female, as designating a gender makes it easier to refer to Nox with pronouns.
A girl would better fit with the seductive and subtle nature of the dark side. I don't take class trailers as canon, however in the sith inquisitor trailer, the inquisitor's voice has a seductive purr that just screams this is Darth ****ing Nox! Nox has also been quite sassy at times with the slapping away of Thanaton's lightning, the arm crossing, the head shaking, the subtle arm movements when forcing Thanaton to his knees, and the backhand lightning slap. Overall Nox fits better as a female and female fits better for this class.