• Space Administrators: can control administrative functions within that space only (look and feel, permission settings for that space as a whole, exports of space content, etc.). Locked page content will not be visible to space admins.
• At the global level, Confluence Administrator and System Administrator permissions govern who can control system-wide administrative settings. Users with the Confluence Administrator permission can perform most administrative functions, but cannot perform functions that can compromise the security of the Confluence system. More on the differences between these two global admin permission types here.
• The confluence-administrators group defines a set of "super users" who can access the Administration Console and perform site-wide administration. Members of this group can also see the content of all pages and spaces in the Confluence instance, regardless of space permissions. See Global Permissions Overview for more information about this super group. 

Bottom line: unless those "admin" users are members of the confluence-administrators group, they should not be able to see an individual page locked via a page restriction.