Comment on Stallion SEO Theme Support by WordPress SEO Theme Author.
Looks like you are using Kontera not Infolinks, see Stallion Theme Kontera In-Text Ads Tutorial where it says
Please note it can take time for the Kontera ads to show up on a site, so don’t panic if it takes a day or two before you see the ads.
Same with Infolinks Stallion Theme InfoLinks In Text Adverts Tutorial.
Yes Stallion works with sub-domains exactly the same as any domain.
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