The unified sources VISTA is a DB VISTA rule, so it's much more flexible than the normal rule. Also more expensive, though. I've used it at several gigs with great success, but may try my luck with marketing channels going forward.
The unified sources VISTA rule reports traffic for subdomains exactly like you describe. It's a pain sometimes because you'll get some domains like stumbleupon.com or craigslist.org that will show hundreds of different referrers to your site. But for the case you describe it would be very helpful. W...