ESXi 5.1.0 build 914609.
I'm not sure if I had health status info available right from the beginning of using 5.1, but I remember I also had to flash the latest bios to my motherboard because I needed support of new-gen cpus...
Anyway if my ST1200BTL (very low-end server board) supports hw-monitoring, your much higher placed S5520HC should support it too.