There is some sort of a referring URL I know of that is logged when the Yahoo! Spider looks at your site. I can't remember but it's something like http://spider.yahoo.com that visits it and that's logged... something like that, as I say I can't remember the actual URL or where I saw it but I'm pretty sure it was in these forums or maybe it was in a newsletter. Maybe someone else can shed some light on this!
When you submit a site to yahoo, they grab the HTML of your page using a spider. This page is on their servers until your site is reviewed. Any images, etc, will be loaded from your site. You can check your server logs for the referrer http://surf.yahoo.com/submissions/ to see if somebody at yahoo has actually looked at your site or not.