It's my understanding that unless your storing/curing/smoking the sausage at temps between 40 and 140, nitrates and nitrites are not needed for preservation. The nitrites will certainly help keep the pink color, but I am not aware of the nitrates doing anything. Always looking to learn. How are you storing your sausage?
I vacuum freeze my sausage for storage.
From the article I posted (link)...What Nitrite Does in Meat"Nitrite in meat greatly delays development of botulinal toxin (botulism), develops cured meat flavor and color, retards development of rancidity and off-odors and off-flavors during storage, inhibits development of warmed-over flavor, and preserves flavors of spices, smoke, etc."
I can't say it any better than that!
Here is a quote from another article:
"Sausages are the second biggest source of food contamination and food poisoning, secondly only to home-canned food products. Ground and moist meat is held inside of the sausage casing and given proper conditions can lead to sausage poisoning. Without proper development conditions, C. botulinum bacteria lay low in a spore form, and can remain dormant for years. To grow, these bacteria require a slightly acidic, oxygen free environment that is warm (40°-120°F) and moist, which is exactly what happens when we make our own meats, especially the smoked ones."
Question: do you check the temperature of the sausage on your pizza before serving it? Do you check the temperature of your refrigerator where you store the sausage? Can you guarantee the meat you just bought to grind was stored properly? Do you sterilize all your cutting boards, knives, bowls, and grinding/stuffing attachments? The botulism toxin is denatured at 185F. However, staphylococcus toxin denatures at 240F. It only makes sense to keep on the safe side of food preparation.
FYI...commercially, ground beef (hamburger) is the biggest offender of food poisoning. Note that nitrates/nitrites are NOT used in ground beef.