ESXi supports a very limited amount of hardware and since that is an older server it probably does not have the driver for that array card. The Hardware Compatibility List (HCL) details all the servers, storage and I/O adapters that ESXi and ESX supports. You should use VMware Server instead which will support it as long as your host operating system supports that array card.
<a href=”http://www.vmware.com/resources/techresources/1032″>Systems HCL</a>
<a href=”http://www.vmware.com/resources/techresources/1033″>I/O Adapters HCL</a>