Downstream in RHEL, we've got a ticket about the rpmdev-vercmp binary missing a man page: https://issues.redhat.com/browse/RHEL-84973
That said, AFAICS, there are currently no man pages written for the binaries shipped by rpmdevtools, not just rpmdev-vercmp in particular.
I'm not sure if there are any plans to provide these but I'm filing this ticket, just in case.