Thanks everybody for your help on this. I've come to the conclusion that this particular hub does *not* require the additional washer and nut. I've taken apart the other hub as well, and it is identical to this one.

SUMMARY (based on responses so far) : Some hubs use dual nuts and a washer, where the nuts and washer w/tabs hold the system together after proper torquing. Other hubs (like mine) use a single, specialized nut, with a flange built-in that seats right against the outer bearing. This is kept from loosening because it is attached with three screws to a housing that is keyed into the spindle.

Take that for what it's worth. If i were an expert, i wouldn't have had to ask in the first place! But know you know everything i do WRT this particular issue.

Please advise if you know otherwise. Thanks.