Schiff appears on Fox because Fox is owned by NewsCorp. And NewsCorp own HarperCollins which publishes Schiffs book. Did you not notice the book plug in that interview?
CNN are boycotting him because he appears on Fox. Its great to see him there though, he really shows up the ignorance of most of the other schills they have on that program. There is more from him here. europac.net/video.asp
It does not always mean he is right though, there was a recent exchange between him and Mish from Global Economic Trend Analysis.
Its cross-marketing the products of other parts of the corporation. Similar to a movie tie-in to McDonalds Happy Meal.
CNN do the same by recycling stories from Time magazine onto their news channel, which is part of the same corporate media giant.
News and media content are products that need to be marketed and generate a return.