Much of New Relic's software runs on FreeBSD, but for some Linux-based agents there are some challenges.
New Relic agents
PHP Agent versions 5.1 and newer support the current Production Release of FreeBSD, on 64-bit systems only.
The monitoring agent for New Relic Servers is a Linux binary, and it may run on *BSD using binary emulation. However, the statistic gathering methods the server monitor uses are totally irrelevant on BSD systems. If anything is reported, it will likely be wrong.