Targeting a RHEL kernel version is quite different than targeting the same official kernel version as they backport a huge number of features, resulting in drivers that may work in RHEL but not upstream, or the reverse
I packaged some python applications in nixpkgs, and it seems the consensus is to try and relax the dependency so that the globally packaged version is used, but if it fails the you can override the version yourself. Though this is not done through the requirements.txt because that file does not have enough information (no integrity hash for example).
