The execution of the UNSKIP procedure is designed to remove SQL Apply filters that have been previously set up on a logical standby database. Based on the provided statements, the UNSKIP procedure is directed to delete any SQL Apply filters for DML statements associated with objects in the 'HR' schema that start with 'EMP'. Since both SKIP procedures had the same schema name ('HR') and statement type ('DML'), and the UNSKIP procedure uses a wildcard (%) for the object name, it will successfully remove both of the SQL Apply filters for 'EMP_NEW' and 'EMP_OLD', as both object names match the pattern provided in the UNSKIP procedure.
Reference:
Oracle's Data Guard documentation and SQL Language Reference provide insights into managing SQL Apply filters on a logical standby database using the DBMS_LOGSTDBY package. This includes adding and removing filters through SKIP and UNSKIP procedures.

Enterprise Manager Cloud Control provides a graphical interface to manage multiple standby databases, simplify switchovers and failovers, and automate failover processes to a specified target standby database. It offers a comprehensive view and control over the Data Guard configuration, making complex operations more manageable.
DGMGRL is a command-line tool specifically designed for managing Data Guard configurations. It allows the administration of multiple standby databases, simplifies the execution of switchovers and failovers, reinstatements, and conversions to and from snapshot standby databases, and supports the automation of failover processes to a specified standby database.
Other options like RMAN, SQL*Plus, CRSCTL, SRVCTL, and GDCCTL do not provide the same level of integrated management functionality for Data Guard environments as Enterprise Manager Cloud Control and DGMGRL.

Transaction Guard provides benefits in terms of transaction consistency and recovery in a Data Guard environment:
* It provides application continuity by rolling back uncommitted transactions interrupted by a failover or switchover (B): Transaction Guard ensures that any uncommitted transactions at the time of an outage are rolled back consistently, thus preserving the integrity of the application's data and state.
* It protects against recoverable errors during a planned or an unplanned outage of a primary database (D): Transaction Guard offers protection against errors that can occur during outages, allowing applications to resume operations more quickly and reliably after recovery.References:
* Oracle Database High Availability Overview
* Oracle Real Application Clusters Administration and Deployment Guide

In the context of Oracle Data Guard and Global Database Services (GDS):
DGMGRL may be used to add the Sales configuration to the Prod pool in gds (A): Data Guard Broker's command-line interface DGMGRL can be utilized to manage configurations with GDS, allowing the addition of Data Guard Broker configurations to GDS pools.
Performing a role change with DGMGRL automatically notifies GDS which in turn activates the appropriate services (B): When a role change is executed using DGMGRL, GDS is automatically notified, and it then activates the services that are appropriate for the new database roles.
DGMGRL may be used to add a single database to the Sales configuration even if Sales is a member of the Prod pool (C): DGMGRL provides the capability to manage individual databases within a broker configuration, including adding databases to a configuration that is already part of a GDS pool.
Reference:
Oracle Data Guard Broker documentation
Oracle Global Data Services documentation