Sorry - I think I initially misunderstood your question...
Yes - using REST API needs to have a user and a free user space.
If you use a named user - that user has to be dedicated to the API (or ensure that readings are done when the user is not logged in to the system).
If the readings are done with a concurrent user - same idea - there has to be a space for the connection.
REST API usage is considered the same as user - just as if you would log in to the system and read / write the data yourself.