Is the Baptism of One Who Rejects a Teaching Valid?
Would the baptism of a person who knowingly rejects an official teaching of the Catholic Church be valid?
Yes. The baptisms by heretics and schismatics are considered perfectly valid (Council of Trent, session VII, canon IV). The minimum faith required for adult baptism would be a belief in the Trinity and a willingness to be a disciple of Jesus. They are not required to have a fully developed understanding of the Faith.
"The faith required for baptism is not a perfect and mature faith but a beginning that is called to develop" (Catechism 1253).