but there is no way with FreeBSD, like there is with
    Debian, to say “never even show me packages that aren’t
    DFSG-free.”

I would be very surprised to discover non-free software in FreeBSD's binary package repository. However, if this is a concern, one needs to set LICENSES_REJECTED in /etc/make.conf, at which point FreeBSD Ports will not build anything with a license that matches. If a company's concerned about the licenses of the binary packages provided by FreeBSD, it could simply set up its own internal binary package repository using poudriere, and use poudriere to filter out software with the unwanted licenses.

See /usr/ports/Mk/bsd.licenses.mk (https://raw.githubusercontent.com/freebsd/freebsd-ports/mast...) for the gory details.