See, though you might feel that getting the first rank in NIOS might be the same as getting the first rank in let's say CBSE or UP board, but according to the government, the certificate issued by NIOS is NOT comparable to that of CBSE or any other central or state board. So, going by this, BITS Pilani (any campus) might not offer you an admission based on your NIOS board certificate.

So, keep preparing for BITSAT and crack the exam successfully. Hope I have answered your question. All the best!