I don't know anything detailed about lore, but in FF12, the Viera were presented as a female-only race, as I recall? Or were the men simply not encountered?

If Viera are a female+only race, then the decision to have them be female-only is by no means motivated by fan-service. However, even if adding male Viera breaks the lore, I have no particular issue with it. The lorehounds might, though. Though the lorehounds would know better than I the lore behind male Viera.