I'm seeing the same thing across a number of Intel Serverboards as well - both Entry Level and SC5520HC etc
It all used to be ok with ESXi 4.1 - so it is more likely to be a VMWare thing than an Intel thing. There may be a BIOS setting which needs to be enabled.
This also applies to the recent Ivy Bridge Intel Desktop Boards which can be used as ESXi 5.1 Labs due to the Virtualisation support - DQ77MK and DQ77KB
Sometimes you get to see Sensor Readings and then at other times you don't.
I'll be patching a couple of Intel environments this weekend. What ESXi 5.1 build are you running?