In previous versions of the Configuring AMQ Broker guide, it clearly stated that a cluster connection was a prerequisite: https://access.redhat.com/documentation/en-us/red_hat_amq/7.2/html/configuring_amq_broker/high_availability#using_shared_store

Prerequisites

1. For master-slave pairs to operate properly using shared-store, both brokers must use the same location to store persistent message data. See Persistence for more information.
2. Master and slave brokers must be part of cluster and use a cluster-connection to communicate. See Clustering for more information on cluster connections.

In the 7.3 and later guides this requirement is less clear:https://access.redhat.com/documentation/en-us/red_hat_amq/7.3/html/configuring_amq_broker/setting-up-broker-cluster-configuring#implementing-high-availability-configuring

After creating a broker cluster, you can improve its reliability by implementing high availability (HA). With HA, the broker cluster can continue to function even if one or more brokers go offline.

While this section of the doc follows the section on creating a cluster, it is not clear that a cluster is a requirement for the HA configuration.