There are no requirements, and I've never heard of countries "being official members of ROS". That would be strange as well, as 'ROS' is a software framework.
As to the image you show: that is the user map as of December 2013, which is rather old, and was made based on user contributed data (so only people / institutions / companies that happened to tell others they were using ROS are shown on it).
For a more up-to-date version, see the ROS Users of the World map that @DLu maintains. It already has one dot for Peru: San Pablo Catholic University.
Note that that map is also based on user input: just submit a Pull Request to DLu/ros_map to get included.
Summary: you don't need to belong to some "ROS club" to be considered a ROS user. Just using it is enough. If you want to show others that you are using it, then you could consider contributing to the ROS Map (linked above).