Start the DC, start a slave (pintsize). Slave connects. All ok.
Shutdown slave, re-connect again

[Host Controller] 20:50:24,691 INFO [org.jboss.domain] (pool-1-thread-5) register host pintsize
[Host Controller] 20:50:24,692 ERROR [org.jboss.as.host.controller] (pool-1-thread-5) java.lang.IllegalArgumentException: There is already a host named 'pintsize'

^C on slave again , then restart slave

[Host Controller] 21:05:54,764 INFO [org.jboss.domain] (pool-1-thread-26) register host pintsize
[Host Controller] 21:05:54,764 ERROR [org.jboss.as.host.controller] (pool-1-thread-26) java.lang.IllegalArgumentException: There is already a host named 'pintsize'

I don't know if this error is spurious or if it prevents some logic from happening.
It should not be thrown when a known domain slave connects to the DC.
Duplicate slaves should be prevented ( JBAS-9186 ) as they create issues.

In RHQ we also have a hub-spoke architecture where the agents exchange a token with the server, that allows them to identify itself. Talk to mazz if you need more info.