Granted, it's true that by nature of being underrepresented, the probability of that one member showing up to approve the comment may be unacceptably low. But I doubt it. In other words, to use your example, as long as the probability is high enough that at least one woman will show up to approve another woman's comment, there shouldn't be a problem.
Personally, I think that this probability is pretty high, though, as pg mentions, this'll have to be determined empirically. For example, it's entirely possible (as discussed in previous threads), that the population of active endorsers are skewed toward certain groups. Or that even a slightly <100% probability of legit comments being seen can ultimately compound systemic biases in the long run.