If you are asking about snack sticks specifically because of the collagen casings I would think you need to put it in a bag to protect the casings, but I have no actual proof behind that, other than collagen casings dont stand up to being boiled.

It seems like a lot of people put the sausage right into the water and I have never been able to do that, something was blocking me mentally. I think I figured it out, I use a Sous Vide cooker and the oils and any bits of meat would be sucked into the Sous Vide unit and cause issues!