Before discussing this question it is important to understand what exactly Project Scope is.
Although certain artifacts and deliverables might not be delivered to the customer, they are still a part of the Project Scope and thus the Project Management Plan (and any other designated artifact for that matter) is indeed a part of the Project Scope
RELATED LINKS
SCOPE MANAGEMENT PLAYLIST
https://www.youtube.com/watch?v=S3UI2u2L1EQ&list=PLLRADeJk4TCKIr–TDiERNdEvqSIMeOBM
SCOPE MANAGEMENT FAQs
https://www.youtube.com/watch?v=Zup8J-IGo_8&list=PLLRADeJk4TCLL5biuiHD3LJN8jpN2jinz
PROJECT MANAGEMENT PLAN PLAYLIST
https://www.youtube.com/watch?v=7DckHLwzEx0&list=PLLRADeJk4TCJWFyNZZhJ8Pm5Ek0ohToOS
SHOP FOR PMP AT AMAZON INDIA
http://amzn.to/2xjhXlS