Hi, i do that.
unRAID and OSX 10.6 (Snow Leopard) as virtual machine in esxi (5.1).
The unRAID vm currently also acts as a host for sabnzbd, sickbeard and couchpotato,
but i want to move those three apps to a dedicated Ubunto or Windows vm soon.
And on the OSX vm i only installed iTunes(for Music and Podcasts) and the Plex Media Server.
The last available version of OSX on media (DVD/USB Sick) was OSX Lion, but i dont think
Apple does sell that one anymore.