If the Sponsor has tasks or responsibilities assigned then it can be considered as part of project team, but generally Sponsor is a person who provides financial assistance and ensures that project and team members are on track.

• Sponsor has an organizational authority equal to or greater than the scope of influence of the project. Generally a sponsor is an executive or member of management and champions the project, pays for it and makes sure the changes are accepted in the business units affected.
• The project sponsor works with the project management team, especially helping with project matters such as Scope clarification , funding,   progress monitoring, and influencing others in order to benefit the project.
• Commit resources from the various business areas
• Participate in major project reviews and approve key deliverables
• Make key project decisions

• Ensure timely resolution of issues affecting project success

•  The Sponsor acceptance required during the close of project and it should be documented as part of the project closure phase.

 On some projects, the sponsor may also be part of the project team. As sponsors have a major share in the project’s success, and therefore, at times, may take an active role on the project team.

Hi,

You can read the following article to understand the role of Sponsor.

Customer is not the Sponsor - http://www.pmbypm.com/an-article-to-provide-some-clarity-on-the-sponsors-role/

BR