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If the 3rd party records are periodically bumped up against your server records to validate the referer records and filter out hits from in-house or other accidental sources, I think you would have pretty good accuracy. It beats having the 3rd party serve the whole page, IMO.
You might also have the third party serve your entire page in a 100% frame -- then the link goes to their server and they get the referer information. However, if their server hangs, then the whole page hangs, instead of just the 1 little dot.