There are persons in the world who do not believe given the actual evidence in the world, but who WOULD have believed had they been given different evidence then they in fact do have.
But how do we know this is true? I think there are two ways to argue for this: 1) Point out that it is incredibly unlikely that all the people (for example) who have been born in a time and place where they never got to hear the Gospel (for example) are by chance, just those people who would not have believed in it
2) People can reliably predict what would not only cause them to believe in God, but also have that belief PERSIST.
The first argument is correct if we assume that an OMNI-God exists but cannot be providential in the world by making it the case that anyone who would believe recieves suffcient revelation, but clearly an OMNI-God could do such a thing so this argument works simply in virtue of not thinking big enough with the idea of God at hand and thus is a failure. The second argument sounds so commensensical. I mean, people will tell that I would believe in God if He did x, y, and z. However, I think modern cog. psychology has shown us that his incredibly commonsensical idea, namely, that people can predict what would change their minds is patently false. For example, what would you predict would make you happier; winning the lottery, or being paralyzed in an accident? Obviously, wining the lottery right? Shouldn't lottery winners be ecstatic and paralyzed accident victims be miserable? Wrong: / Examples like this can be multiplied as well. So, I really can't see that this crucial assumption of the divine hiddenness argument is probably true given the undercutting defeaters above.