Is PRODUCT owner a member of the Scrum Team
Yes because the Product Owners are CONSIDERED to be a member of the Scrum Team. To under stand this we will clear the DEFINITIONS for below two.
(1)Scrum Team
(2)Scrum Development Team
In each Scrum Team there should be a single Product Owner which is responsible for prioritizing work items for the Sprint backlog along with the corresponding acceptance criteria. But Product Owner can be be a member of up to 2 Scrum TEAMS.