Supported or not, I've been compiling Spigot 1.8 just fine on a FreeBSD 10.1 server. There are no issues during the build and the final JAR runs perfectly on my FreeBSD-based Minecraft host. I'm a bit of a BSD nerd, and I generally choose BSD over Linux for my various servers. I've been running a Minecraft server on BSD since the release of 1.1. I started out running Vanilla ultimately migrating to Spigot around 1.4.5 and every change went fairly smooth - with the exception of the original 1.1 map becoming corrupted around v1.4.2. My biggest problem has been replacing all the old pre-1.8 plugins I was running. At least WorldEdit and Essentials are working well.