Oracle linked server shows all tables from all schemas in sql server management studio
Just ran this on SQL Server.  As long as you have the correct USER as the credentials to the linked server, it will give you tables that the User Owns, as well as Tables that the user has SELECT access on.

To Prove this, revoke select on one of the tables to that user (On the Oracle side), and it will no longer show in the query you provided.

REVOKE SELECT ON TABLE FROM LINKUSER;

I just did so and got one less table.  As soon as I added the Grant back, the table returned again in the query.