I thought that was just for partitions? If it's per disk then I suppose it would make sense but HDInstTools sees the entire drive no problem.
I assume usbscsi.device is 64-bit friendy, but your file system needs to be as well. If you're using v40.x FFS, I think you'll run into trouble. SFS and PFS should be fine out of the box, as should a TD64-patched FFS.
Also, you shouldn't need to full format a Flash drive. I've done just quick formats on them and they've worked fine.
