Yeah, looks like mass rebuild just skips these packages: https://pagure.io/releng/blob/master/f/scripts/mass-rebuild.py#_125

I am wondering if it wouldn't make sense to do a scratch build in that case and proceed with normal FTBS policy [0] if it fails.

[0] https://docs.fedoraproject.org/en-US/fesco/Fails_to_build_from_source_Fails_to_install/