Currently, there're no any updates to the Agent for FreeBSD.
AFAIK, The biggest problem is how to reproduce the proc pseudo-filesystem on FreeBSD, or to find some alternative.

For more details, or if you want to reach out to developers, you can check out the digitalocean/do-agent repository, and specially the issue #22 — Build fails on FreeBSD.

While there is a linprocfs comparability layer, that I use to this day, there are agents like CollectD that are open-source and cross-platform plus have a plethora of collection plugins as well as writer plugins. I have CollectD emitting data to a service called SignalFx ( https://signalfx.com ) from process stats, CPU stats, my ElasticSearch, MongoDB, RabbitMQ clusters, down to the ZFS filesystem information. But that's just one option and it just happens to be the option I use. :)