NNPC does not own its own aircraft or employ pilots. They contract their aviation requirements to other companies (Aerocontractors and DANA). If they did employ pilots directly, they would almost certainly be Nigerian. The e-mail is a scam known as a '419', named after article 419 of the penal code and which deals with advanced fee fraud.
If you want to fly helicopters in Nigeria contact Olog, Bristow or Schreiner directly!