If they use a RHEL subscription to support their clients they will be in breach of their contract (not copyright, GPL allows them to do it, but the Support contract doesn't) with Redhat and liable for just as much damages as SAP is going to pay Oracle. I sincerely doubt Oracle is that stupid.
No this move is going to cost Oracle some serious development money to re-engineer all of Redhat's work. When they were just copying Redhat it wasn't much of a concern but now that they are going for the value proposition by trying to provide a "better" kernel Redhat needs to react to make them spend what Redhat does to support their Frakenkernel. With everything provided in detail Oracle could have easily reverse engineered the changes and why there were made and cherry picked what they wanted, now they will have to actually spend money to do that or Engineer their own Frankenkernel from the ground up or provide a vanilla kernel. In the end it's possible Oracle simply won't be able to afford it. Either way Redhat has the marketing position to point out that Oracle's kernel is inferior to their own.
I would suggest that Redhat work with the developers of other good community members (Debian, Kernel developers, etc) to reduce the concern but personally I fully support their need to hurt Oracle's business. I believe that Oracle is trying to kill Redhat to make Solaris more popular. Redhat is a key community member and pays for development of a lot of the key pieces of Linux and the community can't afford for the company to go under. There is no doubt Redhat has done questionable things in the past, but they are probably the best commercial community member and I support their need to remove a parasite.