Magic is magic. All you can do is teach him to have good morals/ethics and whatever he does from there is up to him.
Santeria, in particular, isn't "dark magic" it's just a different religion from general Neo-Pagan paths. In terms of using "dark" magic, that doesn't necessarily mean that it's "bad." There are plenty of ways that sort of magic can be used beneficially, so again, as long as you have instilled a good ethical foundation, I wouldn't worry too much about it. Do you have more concrete examples of what you are worried about him doing, specifically?