......they answer to male Pronouns:|, physically resemble men, and their voices deepen in Puberty they have no concept of a female gender but clearly have one of the male gender, it's canon that they identify as men
from the DBZ fan wiki
"According to an interview with Akira Toriyama, Namekians are hermaphrodites that possess physiques similar to those of human males. Despite the fact that hermaphrodites can reproduce sexually, the Namekians in series are seen reproducing only asexually"
to be fair, Toriyama later contradicted himself and said they were genderless