I think you can simplified this a bit by looking at the hornetq-server resource to get its children names for the connectors resource. 
Something like:

```java
        PathAddress address = PathAddress.pathAddress(operation.get(OP_ADDR));
        PathAddress hornetqServer = MessagingServices.getHornetQServerPathAddress(address);
        Resource hornetQServerResource = context.readResourceFromRoot(hornetqServer);
        Set<String> allConnectors = new HashSet<String>();
        allConnectors.addAll(hornetQServerResource.getChildrenNames(CommonAttributes.IN_VM_CONNECTOR));
        allConnectors.addAll(hornetQServerResource.getChildrenNames(CommonAttributes.REMOTE_CONNECTOR));
        allConnectors.addAll(hornetQServerResource.getChildrenNames(CommonAttributes.CONNECTOR));
        if (!allConnectors.contains(newValue)) {
           ...
        }
```