When you "import library" - per my recollection of the console which is NOT in french (sorry), it is for software packages, and ghost packages should NOT be kept there. Unfortunately, I am not aware of the rules of access for the Software Library, but I am aware that most customers keep this on the same server as the Management Platform is installed.
Ghost images can be imported using the Resource Import/Export tool into Deployment Solution, but they will not appear in the Software Library - they will become packages that are stored in the deployment share (\\SMP_server_name\Deployment) under task handlers\images. For them, UNC is not a possibility, though HTTP access is.
So I am pretty sure you need help from the Software Delivery team who understands the library better than I do. Especially when it comes to finding custom security. :-)