I am still trying to work out how this wonderful solution works? When the Google spiders arrive at a site in the Coop network, and starts spidering the site. Does the spider see an advert on each page or does it see ALL the adverts in the ad_network_ads.txt file? If only one ad per page, then the chances of seeing a link to your site seems low?
It sees the actual ad thats on your site when it visits (check out the source code of a coop members site). Most members have 5 ads plus they have them on every page. Yes, if Google saw one ad it would not make a difference but Google is constantly crawling and if you have enough weight may see 1000's of ads. This all adds up. To directly answer your question, no it does not see the .txt file.