The RPM SPEC file in that repo will have a pointer to the actual upstream sources for the package. This is a typical scenario -- they are not re-hosting all of the sources to build a Linux distro, just the build steps needed to pull, patch, and build upstream sources.
So where do I actually get this upstream (RHEL8) source of say dracut? Because I was reacting to the comment "Red Hat publishes it's sources on https://git.centos.org. Those are then used to build CentOS Linux packages."
rpmbuild will download the sources listed in the spec file, apply the patches, and execute the build instructions to produce RPM and SRPM packages. The SRPM will contain the "as built" source tree.
