So it looks like everything is in order with Alma: recent errata come in with repo syncs, and when I enrolled a test Alma host, made sure to start rhsmcertd, then installed katello-host-tools-tracer, Foreman/Katello correctly reported errata as applicable to the host (with the host status changing to red and everything) and allowed me to go through the install errata → resolve traces → wait a few minutes for the host to turn green workflow that I’m used to with Satellite and RHEL 
That aside, since my employer is currently distro-agnostic for future servers at the moment + compatibility is occasionally better for Rocky on some tools of interest vs Alma, I’m interested in working the Rocky erratum situation. Hopefully this would benefit other folks interested in using Rocky with Katello as well 