Exactly, Qunari women never serve in the Antaam alongside their male kinsmen. They can however become spies and assassins, since that falls under the jurisdiction of the priesthood, so nearly all Qunari women (or female converts to the Qun such as Tallis) that we see outside of Par Vollen are members of the Ben-Hassrath. Further unlike the military, the priesthood is not exlusive only to one gender, but open to both men and women, so you can have male members of the Ben-Hassrath. If Hawke joined the Qun for instance, both genders could be assigned this role, something which is implied a few times by Qunari characters in DA2.
However, I disagree that their were females with the Arishok, since that's essentially two branches at work. He's the leader of the military, so he's got no responsibility towards any member of the Ben-Hassrath, nor any reason to have them aboard his ship. It's possible that they did go along and he simply didn't bother to save any of them from drowning (since it's not his role, so not his problem), but if some of the men in the Qunari compound are Ben-Hassrath who went along, why they didn't save any of their female comrades? It therefore makes more sense that it was solely a military operation.
Didn't the above poster already provide an official source straight from the developers own mouth (you can't get any more Word of God than Gaider), where he posted that he asked Mary Kirby about it and she gave the definition of Vashoth as being a "Qunari born outside the Qun."
I know all of this already.
Women are blacksmiths, they make clothes, armour. All smiths who accompanied Arishok drowned prior to DA2.
Save them? In a storm? How?
Kossith-race spies are rare due to a pretty simple reason: they are too noticeable. So qunari spies, even female, are likely to be of other races. It's not impossible for benhassrath to go to bas lands, but likely they would send elf or human ones.
So my point stands, it is interesting to know how Adaar's mother managed to escape. I think it is most likely she was from Rivain - it's much easier to escape there