What is the difference between the using Cloud Platform Service Broker and using Alias IPs when configuring Kubernetes Engine?
Service Broker doesn't have anything to do with Alias IPs. Cloud Platform Service Broker is called by "Kubernetes Service Catalog" to get GCP services provisioned with Kubernetes manifests (for example, you can create a Cloud SQL database by deploying a Kubernetes manifest thanks to this feature). Alias IPs don't have anything to do with this.