Can a Service Broker be provisioned for custom apps, or are custom sw modules required for each specific customer application?

In general, Service Brokers can be provisioned such that they support multiple applications generically, without requiring a custom software load on the service broker.  The service broker may host supporting service logic to support a custom call flow or service interaction, but the underlying software will be generic.  Depending on the implementation and/or vendor, the supporting service logic may be written in JAVA, C++, or XML definition files.