The reason some dogs aren't registered has nothing to do with finding out a persons address. It's either a dog from unregistered parents, Mal's and Dutchies and sometimes GSD that for structural reasons are not registered as they will never be used for breeding, ie, monorchid, missing some dentition, floppy ear, etc (dual purpose or patrol dog) or in the case of narcotic or bomb dogs, they are often times dogs from all over, shelters included and they wouldn't be registered either.
But either way, LEO's usually are not the owner of the dog until it is retired, the Department is the owner, and who doesn't know how to find out where the PD is???