Mixing OS types is not recommended, that said CentOS and RHEL are mostly aligned and it should work, and you want to ensure the kernel level is supported. BUT if you don’t follow best practices, you then take the risk, in terms of something not working due to OS specific configuration/libraries, package management/file systems/performance etc.
Most Enterprise’s standardise, so they have baseline OS config as standard, and ensure that the hardware and software requirements are met for Splunk.
There is a table here of the kernels level support
https://docs.splunk.com/Documentation/Splunk/9.2.1/Installation/Systemrequirements#Supported_Operati...
