Do they use their servants as guinea pigs, or for performing magical rituals? I don't think so.
They won't just let a slave be used for blood magic – it's too expensive. So, the probability of being used for blood magic is no higher than the probability that in Orlais, a knight will seduce his daughter, in the Free Marches a bandit will kill him, or he will suffocate in poverty in Antiva, or that he will be sold into slavery to assassins with their deadly training programs, etc.
In terms of military strategy, by the way, they don't excel either; it's a pity that the Qunari aren't interested in their destruction at the moment.
Where do we end up when we save the world?