Dear Seema, now NEET is the entrance examination for admission into Medical, Dental and Ayush colleges acrpss India. The other 2 tests are JIPMER and AIIMS. For NEET, Open school students are eligible if they meet the minimum aggregate and age criteria. If they get a seat through NEET in a Government Medical college, they are eligible to study Medicine from that particular college because NTA, the exam conducting authority for NEET has recognised NIOS students to be eligible for NEET. 

Hii

All the government colleges in india offer admission to MBBS course based on the scores of NEET.
In NEET Examinations, it is clearly mentioned in the guidlines that students who have passed 12th class from Open School or as private candidates are not eligible to appear in NEET. 
Also if a candidates has studies biology/biotechnology (which ever is applicable) as an additional subject at 10+2 level, are also not eligible to appear.
SO, no NIOS students can not get admission to government medical colleges.

Hope this helps
Thanks!!