I set up a campaign with Yahoo to test some direct linking. I have 50 keywords, search and content match and $0.5 for search/ $0.2 for content. So why is Yahoo telling me no impressions? I have enabled everything I can think of. Google gave me 100,000 daily impressions for the same keywords.
Check your settings to be sure that you've not set your targeting wrong, etc. Also make sure that everything is showing as active. The campaign/ad group could appear active while the ad itself is still "editorial pending." Check the ads page itself to see if the ad is still pending. If everything looks right to you, fire off a support email to Yahoo.
You say 100,000 impressions on Adwords but this is likely almost all on the content network. Yahoo's CN is not quite as extensive or as good as Google's so that's one reason. Compare search impressions on both networks. I would expect Yahoo to get about 20-30% of Google's impressions but this can vary wildly by industry.