Право на обновление таблицы пользователю дано? Если дано, то как напрямую или через роль?

>а это ведь уже не важно? Процедура отрабатывает с
>правами владельца схемы.

Нет не так. Вот из Доки (Oracle8i Concepts/27 Privileges, Roles, and Security Policies):

Invoker Rights

An invoker-rights procedure executes with all of the invoker's privileges. Roles are enabled unless the invoker-rights procedure was called directly or indirectly by a definer-rights procedure. A user of an invoker-rights procedure needs privileges (either directly or through a role) on objects that the procedure accesses through external references that are resolved in the invoker's schema.

The invoker needs privileges at runtime to access program references embedded in DML statements or dynamic SQL statements since they are effectively recompiled at runtime.