Who owns them now?
Yes, the -Name parameter expects a string. You could create an array and pipe that to set-nadiskowner. It's possible to be a bit more creative as well depending on what you're trying to do. Get-nadiskowner returns objects that include a -Name property, a string, which is the name of the disk. On set-nadiskowner, the -Name parameter accpts pipeling input bypropertyname...
Let's say that I add a new shelf and want to assign all the disks to a specific controller, controller1:
$controller1=get-nacontroller controller1
get-nadiskowner -OwnershipType unowned | set-nadiskowner -Controller $controller1
Or perhaps I have a shelf that came from another controller and have now attached it to controller1 and wish to take ownership of all the disks with unknown ownership and assign them to controller1:
$controller1=get-nacontroller controller1
get-nadiskowner -OwnershipType Unknown | set-nadiskowner -Controller $controller1
J