Yes. You may work on your prerequisites for the nursing program while simultaneously working on your GED certificate. Prerequisites for the nursing program generally take one or two years to complete. Work with your academic advisor to develop a schedule that will allow you to reach both goals - a GED certificate and admission to the nursing program.
The nursing program itself is a very busy program, and working on a GED certificate while actually enrolled in the nursing program may be too much coursework to handle all at once. While a GED certificate is not required for entry into the nursing program, it would be advisable to attain that certificate before admission to the nursing program.