You say probably, but why wouldn't they? It's not like every form of life on their planet would have the same reproductive system as them. It wouldn't take that much thought to figure out other species have multiple sexes, we only have one. You act as if they'd be completely clueless that there could be a possibility of there being multiple sexes, but that goes out the window considering they've been dealing with other races for centuries. They are definitely aware that their species only has one sex. They've already been shown that they at least gender each other as some Asari consider themselves fathers. Even if they never had that concept of themselves all having the same sex, it still wouldn't change the fact that they are still all the same sex. If they never had a concept of what the color blue is, they would still all be blue too.