The very least the second shooter should be able to do is to display the images as his own work. Copyright ownership should be transferred to the primary photographer, but then licensed back to the second photographer for portfolio display (not for sale, or editing, etc).
The second shooter doesn't have a model release or permission from the couple to display it on their website. That and couples might not like finding photos of themselves popping up in random places. I wouldn't. Remember we're dealing with regular people here, it's not a generic wedding photo, it's two people and a day that's very special to them.
That's why I give the second shooter permission to display their images in a printed portfolio, but not online or publicly.