Last time(2008) I dealt with Oracle support in regards to linux, they did provide support for CentOS, but funneled customers to oracle linux. IMO they have a good model for helping ensure oracle linux doesn't become a fork of redhat, by creating emergency patches on their side, then sending code/reasoning to redhat to get included CentOS/RHEL. They are helping the quality of redhat's product as long as they get good margins on support contracts.