ArcGIS relies on the connecting user and its schema name to be the same. Microsoft SQL Server and PostgreSQL do not have this requirement. If a connection is made from ArcGIS for Desktop to an existing table in a SQL Server or PostgreSQL database as a user who has privileges on the schema the table is in, the data can be viewed but cannot be managed from ArcGIS for Desktop.
For example, if all the tables in a PostgreSQL database are stored in the public schema, the data can be viewed in ArcMap, but tables cannot be analyzed and privileges cannot be granted on them from ArcMap. Additionally, tables cannot be truncated, data cannot be loaded to them, and columns cannot be added to, removed from, or renamed in the tables from ArcMap.