NIOS is a GOI recognized body for open schooling and is also recognized by University of Delhi. So if you have done a subject in Mathematics from NIOS then you have nothing to worry about it and you are perfectly eligible for the DU JAT examination. The basic eligibility criteria is that the Candidate should have scored at least 60 percent marks in aggregate in four subjects that include Mathematics, English, and any other two subjects.

To know more about the DU JAT visit the link below:

https://bschool.careers360.com/articles/du-jat

I hope this answer helps. All the very best for your future endeavors!