Funny that VMware ESXi4 does not support the CK804 Nvidia controller. It is a standard on many Opteron Server Motherboards. Also interesting that XenServer supports it just fine. If anyone ever finds a fix or workaround, please post it...
ESX doesn't support software RAID (a.k.a. fake RAID,) which is what the CK804 is. Also, ESX doesn't support SATA drives for datastores anyway. While it works and many people use SATA drives (especially for non-production systems) the throughput of a non-cached SATA controller is often quite poor.
...Going the USB stick route is not as reliable as a SATA controller.
The USB drive is only for the boot files. A server booting from a USB drive and having all it's datastores on a SAN means that the server has much less moving parts and much less heat. (i.e.: no hard drives.) So one could argue that such a server could be more reliable. In addition, I usually just preconfigure a second USB stick for DR. But really, reinstalling ESXi only take a few minutes if your datastore is separate from your boot disks.
While the T105 is a low cost server so it would seem on the surface that a typical owner of this server wouldn't have a SAN, I argue that a low cost SAN is actually a good fit here. Build an ESX server to boot from USB. Then build a second machine to act as a SAN with either iSCSI or NFS. For example Openfiler or FreeNFS have support for software RAID and will install on "throwaway machines" so you still have low cost. This way, the only thing that needs to be on the ESX compatibility list are the NICs. The hard drive controller/RAID controller can be almost anything you want, since it's not in the ESX machine. And like I said above, having the datastore separate from the ESX boot partition means that reinstalling ESXi almost trivial.
I run such a setup for my test environment, except my SAN is a Windows 2003 server with iSCSI and NFS. One of the advantages with Windows as the SAN is that I can install the vSphere client this SAN machine. But also the often posted request of "how to copy ESX VMs to USB drives" is trivial with a Windows SAN as the primary datastore. 