if you send traffic to a cj advertiser via your affiliate link then yes cj does know the referring url. epn/ebay is not with cj anymore, and yes they can tell as well where the traffic comes from.
Not only does EPN know where your traffic is coming from, it is terminating partners right and left who are referring worthless traffic. Bottom line, don't buy or trade for traffic that's phony. EPN want's real shoppers. Make certain you're sending quality traffic.
From your perspective it might be exceedingly high quality traffic. But I doubt if its viewed that way by EPN. Good question, though. Why not ask them? For my own part, with affiliate sites like those geared to EPN, I view it as practically worthless from the standpoint of conversions or ACRUs. You might get a few backlinks out of it, though. In thinking about it, I doubt that EPN would terminate you for it, since you have no control, in theory, over who bookmarks your site(s). Great strategy - eliminate your competition by stumbling them every five minutes.