These are pets, not zoo display animals. As pets, these animals disserve an environment that will maximize their life, keeping them happy and healthy for as long as possible. To this end, we should choose a substrate that is more suiting for a pet...than a wild dragon, because as has been posted, a dragon’s lifespan in its "natural" habitat is significantly shorter than your typical pet bearded dragon.
In my opinion, natural stone or ceramic tiles are the best compromise between a "natural" look, and animal wealth fare. Loose substrates such as sand not only pose an impaction risk, but will harbor bacteria and parasites which can harm you and your dragon. As has been posted before, bearded dragons live on hard pan, not sand. If you have ever walked on the stuff, it’s like walking on concrete...where the sand thing came from, I don't know.
So to answer your question, sand is no good. Not only is it an impaction risk, but its a bacteria/parasite breeding ground, and if that wasn't enough, its not even a dragons natural envirnment.