Yes. It will not track the unique, however, if you just add the ?nats=xxxx. You must use /track/NATSCODE/ to track uniques and referrers.
To track the uniques, use the link provided in the affiliate area, ie
http://join.sitename.com/track/NATSCODE/, and add the rest of the url youre trying to get to, ie
http://join.sitename.com/track/NATSCODE/models.php
If youre trying to link to a subdirectory or need to pass other parameters, it also works. For example:
http://join.sitename.com/track/NATSC...dels/Alana.php
would track and redirect to
http://www.sitename.com/models/Alana.php?nats=NATSCODE.
http://join.sitename.com/track/NATSC...hp?var1=value1
would track and redirect to
http://www.sitename.com/models.php?n...DE&var1=value1
Hope this helps.