you actually asked 2 different questions this one being the most important i think !! question #2 = please i need to know if Rhce is useful in Nigeria http://www.redhat.com/training/certifications/rhce/ link talks about RHCE this answer to question 1 is obvisous
If you are trying to decide on a career move or path then this post would have been better in the Community forum. People would have understood its context better.
As Redhat is a popular version of Linux, if you receive formal training and qualifications with it there may be some good opportunities for you. Try Googling phrases similar to this, "linux jobs in Nigeria", or, "Redhat jobs Nigeria". Alternatively, you could find a local Job Agency (they recruit people for companies in a temporary basis) and ask them what the demand is for people with Redhat/Linux qualifications.