The floating resistors would more or less just put a load on the bus - with only a few devices that might be forgivable but I wouldn't really try. But I've never seen passive terminators that could be disabled with a jumper.
Your termination schemes are correct, without the backplane board you'd still have to terminate both ends of the SCSI chain - if only one host adapter connector is used, the other needs some kind of terminator.
I usually disable all passive terminators I find and replace them with active ones, that can be switched much easier.