UPDATE:
Turns out the issue was unrelated to the SDR module. I was simply missing python3-cheetah and python3-ephem packages.
I'm going to have to bug the rpm package maintainer for python3-ephem as it isn't in EPEL 9 repos yet. For now, I've added the package to the copr repo I linked earlier.
I've got weewx w/ SDR and MQTT modules up and running on Rocky Linux 9. I'll continue to monitor it, but it seems to be running well!