What is the status of St. Hildegard's visions, and if they are from God, would that make them infallible?

Well, close to it. And that's why you really can't say they're really from God, because you don't know. Approval doesn't mean that everything in the vision that was said is true. That's not what it means to be approved by your bishop. It's just like an imprimatur for a book. It doesn't mean that what the book's saying is necessarily true. It just means there's no error in it from a dogmatic perspective, because the church can't teach error.