@Sebastian-Roth You have to remember that memdisk only works for bios based computers. FOG does not ship a uefi compatible version of memdisk. Also with memdisk that 2.7GB iso image needs to be transferred and fit into memory on the target computer.
As I said if that IS the SUU disk it may not support netbooting. BUT on the PE620 if you use the lifecycle controller to update the system I know you can update the system from a USB stick with the files on it as well as link to an external repository. I just can’t remember at the moment if NFS is supported. I know ftp and CIFS is supported. If its NFS then the OP can just unpack the files in /images and access them via the lifecycle controller.