Dear Aspirant

Yes, NIOS students are eligible for AIIMS 2019 as one of the eligibilty criteria for appearing in entrance is that candidate should have passed the 12th Class under the 10+2 Scheme/ Senior School Certificate Examination (CBSE) or Intermediate Science (I.Sc.) or an equivalent examination of a recognized University/ Board of any Indian State (here comes NIOS) with ENGLISH, PHYSICS, CHEMISTRY and BIOLOGY as subject. 

Hope this helps you.