You would need to be actually ethical rather than marketing ethical - I don't know you so I don't know if you know the difference. Certainly there's no shortage of Silicon Valley "characters" who don't.
It's a very powerful "good news story" to sell to potential clients:
--> lower cost workforce
--> positive life benefit for the African people, lifting people to better lives
--> western style work protections at African costs
--> "publicity positive" for buyers versus "publicity negative"
You would not believe the power of "lower cost workforce" in gaining new clients.
If you know a bunch of African programmers then it should not be hard to find work for them at $x/hour to western clients.
Any employer that wishes to show it cares for African people and wants to help them to a better life really SHOULD be buying services from your new company.
Remember in places like Australia, the banks - who are the biggest buyers of outsources international programmer resources - would consider $40/hour to be an absolute bargain.
It's not a zero-sum game - you don't have to treat people like trash to get any value out of their labor.