It seems to me that it is impossible to configure slave HC to connect to master DC using configured secret key.
When slave HC is trying to reach remote DC it fails with:

[Host Controller] 13:11:55,573 ERROR [org.jboss.remoting.remote.connection] (Remoting "f16:MANAGEMENT" read-1) JBREM000200: Remote connection failed: javax.security.sasl.SaslException: Authentication failed: all available authentication mechanisms failed
[Host Controller] 13:11:55,606 ERROR [org.jboss.as.host.controller] (Controller Boot Thread) JBAS010901: Could not connect to master. Aborting. Error was: java.lang.IllegalStateException: JBAS010942: Unable to connect due to authentication failure.
[Host Controller] 13:11:55,690 INFO [org.jboss.as] (MSC service thread 1-2) JBAS015950: JBoss AS 7.1.1.Final-SNAPSHOT "Thunder" stopped in 38ms

I am using stock domain.xml, host-master.xml and host-slave.xml updated according this documentation:
https://docs.jboss.org/author/display/AS71/Securing+the+Management+Interfaces

1) I have added slave/slavepassword user to ManagementRealm
2) U have updated host-slave.xml to identify as "slave"
3) I have generated base64 encoded "slavepassword" passphrase and added as a secret key to host-slave.xml