I can verify that (at least) the WB is showing CW promos on the network feed because of something hilarious that happened with my own WB-turned-My Network affiliate, Seattle's KTWB. A few weeks ago I was watching that station specifically looking for My promos. A commercial break was rolling along, and they came out of an ad for some block of comedies on that station... and for a split-second before the regular show came back on, there was a big green screen with a CW logo and something else. I had to imagine the people at the station knew the CW promo was coming and intentionally placed the local ads to cover it up... the split second they didn't get was just mind-boggling.
Does anyone know if UPN is showing CW promos on the network feed too?