dear student

Yes, as per my knowledfe you can surely apply for admission in DU after completion of your 12th from NIOS board, there is nothing to be worried in it. 

 As NIOS certificates are valid and recognized and at par with other national and state board of education. To get admission in Delhi university one must check the eligibility criteria and cut off marks.

hope this helps

All the best!!!

Therefore, your only concern should be of marks and not that from which board have you completed your 12th in.