Extract Admin OG members from basic page with views
I found the solution by doing the following

In Relationships

OG membership: OG membership from Node
(OG membership from node) OG membership: Group Node from OG membership
(Group node from OG membership) OG membership: OG membership from Node group
(OG membership from node group) OG membership: User from OG membership
(OG membership from node group) OG membership: OG Roles from membership  

In filters

(OG Roles from OG membership) OG user roles: Role Name (= administer member)

The idea was to select the roles from the OG membership of the Group.