If the table is not registered 1. it is not possible to valuesets 2. it cant use the "who columns' 3.we cant go for the flexible segment columns(attributes segments)
and if it is registerd in app u can automatically populate the data in apps
We register a custom table in the custom schema. Then give all permissions to APPS schema. Reason being when stored procedures or functions are written to perform DMLs on the custom table it is done from APPS schema.