I was wondering do CentOS bug fixes get pushed upstream to RedHat or Fedora? I imagine it's up to the maintainers of RHEL/Fedora, but I wanted to know the direction bug fixes get applied between distributions.
It's the other way around, the bug fixes for CentOS come from upstream at Red Hat.
Typically you get CESAs like this
Not really Fedora bugs are pushed into RHEL, RHEL is kind of derivative from Fedora suitable for enterprises. Bug fixes, documentation and a good stuff of CentOS comes from Red Hat.
CentOS is essentially another version of RHEL which does not include paid support and no timeline of bug fix.