Is cloning moral and useful in The House of the Scorpion?

On the whole, you'd have to say no. In The House of the Scorpion, cloning allows a notorious drug lord to extend his natural life, which of its very nature cannot be anything other than morally indefensible. If that weren't bad enough, this highly dubious procedure creates an entire group of people deliberately handicapped from the start of their lives and who will never be able to reach their full potential.
Cloning may be useful in the sense that it keeps a reliable partner of the United States government alive. But in moral terms, the continued renewal of El Patron's life is problematic, to say the least. For as long as he is alive, the vast opium fields of Dreamland will continue to be cultivated, thus leading to even more drug addiction, with all its attendant miseries, for millions of people across the globe.