Can a marriage be called valid if a Muslim girl marries a man reverted to Islam and had Muslim mother and Hindu father
The faith of the relatives of the spouse isn't a condition for marriage.
Allah says in the Quran (2:221):
And do not marry polytheistic women until they believe. And a believing slave woman is better than a polytheist, even though she might please you. And do not marry polytheistic men [to your women] until they believe. And a believing slave is better than a polytheist, even though he might please you. Those invite [you] to the Fire, but Allah invites to Paradise and to forgiveness, by His permission. And He makes clear His verses to the people that perhaps they may remember.
As seen from the verse, it is the faith of the would be spouse and not that of his/her relatives that Islam is concerned about.
Also w.r.t Jews, Christians and other people of the book:
This day [all] good foods have been made lawful, and the food of those who were given the Scripture is lawful for you and your food is lawful for them. And [lawful in marriage are] chaste women from among the believers and chaste women from among those who were given the Scripture before you, when you have given them their due compensation, desiring chastity, not unlawful sexual intercourse or taking [secret] lovers. And whoever denies the faith - his work has become worthless, and he, in the Hereafter, will be among the losers. Quran (5:5)