The CGFNS Certification Exam is just a "screening" test for graduates of foreign nursing schools. Passing it doesn't grant you the priviledge of obtaining a nursing license in any state in the US. Since you are going to be a nurse practitioner student, you will be required to obtain a license as a Registered Nurse before your nurse practitioner clinical placements begin. Wayne State University may let you register for non-clinical courses without a Registered Nurse license but it will be imperative that you be licensed once you step foot in the clinical setting and provide care to patients as a nurse practitioner student.
Since Wayne State University is in Detroit, Michigan, you will need a Registered Nurse license in the State of Michigan. The Board of Nursing in that state requires foreign trained RN license applicants to show proof of either passing the CGFNS Certification Exam or submitting a CGFNS Credential Evaluation Service and passing a test of English Proficiency (TOEFL, MELAB). This is per this link
from CGFNS. In your favor, you're already taking the Certification Exam because Wayne State requires it for MSN students with a BSN obtained from a foreign country. If I remember it right, Wayne State also requires passing a test of English proficiency such as TOEFL or MELAB if you are trained in a country where English is not the language of instruction.
Incidentally, I am licensed as an RN and NP in Michigan but have move out of state since 2009. I've noticed that the web address for license applications have been changed and is not very user friendly now. It also appears that applications are now processed completely online instead of how it was done in the past which was through a paper form that could be downloaded and printed from the website. I also noticed that the website is now asking for a US Social Security Number or SSN in order to create a profile which leads me to believe that Michigan now also requires a US SSN for RN licensure applications.
I am also an alumnus of Wayne State University. I obtained my MSN with an Acute Care Nurse Practitioner concentration there.
Below are the web addresses pertaining to the information I provided above: Link to Michigan Public Health Code regarding licensure of foreign trained nurses Link to Web Address for RN license applicants