1--Shadow Mountain is a national secular imprint of Deseret Book. Orson Scott Card often publishes through them.
2--Walmart is a very hard place to get into for books. It's the "mass market" segment, and they don't want to take books unless they know it's a broad sell, nationwide.
The Walmart in Orem has a lot more books than most Walmarts I've seen, and I imagine the LDS content is because they have regional buyers--they might place more LDS content in places that they know LDS people will buy it--across a broad region. Perhaps LDS people are also more likely to look for discount books?
At any rate, the Walmart generally tends to be homogeneous across the country, so maybe that's a regional sales thing, specific to that store, controlled locally? I don't know. But it is definitely hard to get into the mass market retail stores for books, because there's so little shelf space. Very few SF/F books make it there--I usually only see Stephen King, a whole bunch of romance, and the latest John Grisham/John Le Carre/etc.