Reactor classes are derived from AcRxObject, not AcDbObject. Because these reactors are not database objects, ownership does not apply to them and they don't have object IDs.
Different kinds of reactors receive different types of notification events. A database reactor (derived from AcDbDatabaseReactor) receives events related to the state of the database—for example, when an object is appended to the database, modified in the database, or erased. The reactor's notifier is the database, so it is added to the reactor list of the AcDbDatabase. An object reactor (derived from AcDbObjectReactor) responds to events at the object level, such as copying, erasing, or modifying an object. It can be added to the reactor list of any AcDbObject. An editor reactor (derived from AcEditorReactor) responds to AutoCAD ® -specific events such as loading and unloading a drawing, starting or ending a command, and other kinds of user interaction. The AcEditor object is the only notifier for an AcEditorReactor.
For a complete class hierarchy diagram for the reactor classes, see the Notification section of classmap.dwg in the ObjectARX ® classmap directory.