Yes, NIOS (National Institute of Open Schooling) senior secondary certificates are recognised as equivalent to CBSE and state boards for railway recruitment.
The official notification only asks for a 12th pass from a recognised board, and NIOS is a recognised national board.
During document verification, your NIOS marksheet and pass certificate are treated the same as any other board’s.
Make sure your name and date of birth on the NIOS certificate match your other documents.
If a specific notification ever excludes open schooling, it will say so explicitly in the eligibility section.