@RandyHall, are your sure that $this->getCurrentCategory() will get the category from the same place as $layer->setCurrentCategory($cur_category); will set it to?
Watch the source code here and here. As you can see category is set to the layer model and get returns category from registry(via call to block).
So I would suggest you to do something like this:
$_img = $layer->getCurrentCategory()->getImageUrl();