Yes, NCL is quite clear on what is allowed. Perhaps a rental would be a good idea. Here is the info about that:
For additional details on the prearranged rental program for wheelchairs, scooters and other medical equipment, please contact our authorized vendor. Please note that the other vendors will not have access to Norwegian ships:
Scootaround
Phone: (toll-free) 888-441-7575 or 204-982-0657
Fax: 204-478-1172
www.scootaround.com