Supermicro X8ST3-F is working fine with ESXi 4.0 ...
ESXi must be installed with the version 4.0 stuck. I spent about 35h just to figure out that the version 4.0 with Update 1/2 and version 4.1 cannot be installed, but it works fine if the 4.0 is installed and upgraded to it to 4.1.
I installed ESXi on a USB key, from another USB key, and it works too.
I did not tried to used the onboard Software RAID, but it works fine with the RR4322 controller from Highpoint after installing the provided drivers.
I also attached a 12array DAS 1280 with integrated SAS Extender to it, from Habey (http://www.habeyusa.com/products_show.php?id=308