I think he is smoking store bought sausage, that he is not sure if it has nitrites in it.
My understanding is that nitrites are used to prevent botulism spores from producing toxins, which happens in moist, oxygen free environments at temperatures between 40* F and 140* F. That describes what goes on inside a meat smoker perfectly. Smoked hams, bacon and smoked sausages etc. get the nitrite (cure by another name). Put another way, if it doesn't have nitrite in it, you don't smoke it for this long at these temps. You might grill it, but not "smoke it".
Unless you are willing to take a chance on botulism poisoning, if it's smoked at these temps for this long, you would want to be sure it has sodium nitrite in it.
The pink color, etc. are side effects. That is a pink color all the way through. That is different from a smoke ring, which forms on the outside.
BTW, if you want to enhance the smoke ring on your pulled pork, briskets, etc. put a little insta cure #1 in your rub. It's cheating, but makes the outside bright pink like a smoke ring. It's not for "cure", it's just that pink side effect working on the surface.