use admin theme to render modules pages
I found 2 solutions to this:

Solution one

Use hook_custom_theme(): see hook_custom_theme()

function mymodule_custom_theme() {
 $use_admin = workout_when_you_want_to_use_admin(); //true or false
 if ($use_admin)
   return variable_get('admin_theme');
}


Solution 2 (preferred)

Ensure that the user account has the permission View the administration theme attached to their role.