So let me spell it out to make sure it's very, very clear.
When a customer purchases Oracle Linux support subscriptions (Basic, Basic Limited, Premier, Premier Limited) or purchases an Oracle x86 server with Support, they have the full right-to-use included for Oracle Clusterware without any additional fees. There is no requirement to have another Oracle product in this cluster. There is no additional fee for a high availability option for Oracle Linux, it's included.
This Clusterware is the software used as part of Oracle Real Application Cluster (RAC) and is a very solid highly scalable, feature-rich clusterware. You can write your own extentions for your own applications or use some of the existing extentions out there for other apps.
There is no additional fee. In fact you can see this on the clusterware homepage as well.