this is a quote from mattg @ dish "Netgear 802.11N model WNDA -3100v2 is the model number we support."
so as long as you get that particular one no it does not matter where you buy it.
We have had this discussion before. Some people have reported success with other adapters but some others have not. If you happen to own one or you are a gambler by nature go ahead and try it but if you want greater certainty order the model described through DISH or some other retailer.
Dish sells the Netgear unit, guaranteed compatible, new, shipped second day air, for $25. Most places sell it for, at least, twice as much. For once, Dish has the real deal.