I would expect the kernel version to largely not matter to Splunk as long as it is relatively modern - that is supports things like NPTL (New POSIX Thread Library) which was a kernel 2.4 feature. The kernel maintainers go to a substantial effort to make sure that no kernel changes break existing user-mode code, and Splunk does not have anything that runs outside of userspace. Sometimes though, the maintainers do mess up and a substantial flap1 comes of it.
But, now be warned of the difference between 'runs' and 'is supported'. If there is a problem, it will be up to Splunk support to decide if they want to commit to supporting these newer kernels at this time.