Can a Muslim person be an witness to sign for Marriage certificate of Hindu people
Yes he/she can as it is a matter of giving witness to see a fact. And telling truth (if needed in future) is a fundamental pillar of any religion/s.
Yes, a muslim person can be a witness for hindu marriage.
Yes, a Muslim can be a witness even for a Marriage of Hindu, and there is no bar in any Law either in evidence Act or Hindu or Muslim Personal Law barring a Muslim to be a witness.
How ever in Mohammedan Law for Muslims the evidence of two Muslim women will be treated as one.
So if your case is decided in court of India whether be Muslim men or women one witness is sufficient. If it is in Middle East Countries where Islamic Law strictly followed One Muslim man is sufficient if Muslim woman two to testify.