Since Hope is damaged, the leash on Silent Hill will be loosened anyway- Fear would be more than happy to tip that over to allow the monsters within to run free. Sharon's reality shifting would be fine as well, though of course there'd be reasonable limits on it- she couldn't affect the entire city at once and it would need to be somewhat localized to her general location.

Of course, the Null do not feel fear, so Silent Hill wouldn't have much of a psychological effect on them, but they can be physically affected by whatever forces might lurk there!