I have used wild components in some of my freshwater tanks with nothing but disasterous results. Everytime I added stream-gathered plants, I either got parasites or fugus bloom... even after soaking the plants in dilute bleach.
If the only wild element you are introducing into your tank is the sand, then skip it. Theres no sense in contaminating everything else you have spent money on.
This is just my paranoia from past experiences talking. There is a good chance you can use the sand with no ill effects. Just be prepared for problems.
ps- maybe if you boil the sand you can reduce your chances of introduced contaminants.
ps- certain gram positive strains of pathogens produce endospores, and even boiling will not kill them.