The official way: Install ESXi 4 on an USB flash drive, then install 3ware 9650SE & 9690SA driver provided by 3ware (driver is not certified yet, but seems to work).
The unsupported way: Add a custom oem.tgz during installation; this way you can install ESXi directly on a 3ware volume.
However, proper RAID monitoring and management is still unavailable - even tw_cli in the unsupported console does not work (the 64-bit version does not start at all, the 32-bit version starts and complains that the kernel is 64-bit). :smileysad: