Can I use Dvorak on a physical keyboard?
If your phone is rooted I think that you can write your own keyboard layout. I'm using my own layout (on SGS I9000) for some Chinese blouetooth keyboard that I bougth recently.

Layout files are in /system/usr/keylayout/ directory. Layout file that is used by my keyboard is Broadcom_Bluetooth_HID.kl. I think that layout used by built-in keyboard will be qwerty.kl - you could modify it and check if it's working.

Remember to make backups of original files before changing it...