Enemies who are only enemies by circumstance wouldn't be the right fit for the exchange, since at least one character in the ship has to have a negative opinion of the other - but as long as one character in the ship does have a negative opinion of the other, it's fine if they're also having sex. The "hatred" can be a deep personal dislike informed by years of intimacy or it can be a series of shallow and mistaken assumptions/prejudices/stereotypes, also. And we won't be personally interviewing participants about their noms or checking works to make sure there's enough hate in them, so if you think the enemies-to-benefits stuff you want to request/offer involves at least one person hating someone, then we're happy to have it in the exchange!