Weathered100 First, great question! Second, Parksider , as usual, is correct. Adding cure to a meat product is going to retard the growth of botulism spores but it is not going to make the meat safe to eat by itself, it still needs to get to 160° to fully kill off any harmful bacteria growing inside it. The same is true with Smoked Meat Stabilizer, it speeds up that conversion of Nitrite to nitric oxide faster than E. Coli can grow but it won’t kill it on its own, it still needs thermal processing to make it safe to consume.
As far as moving it to water, I have never done it but there is no reason it would not work and with a summer sausage the only “smoke” you would lose is what has accumulated on the outside of the fibrous casing. As you don’t eat a fibrous casing, this will not affect the taste.
I would vac pack it first just to be sure but I also don’t think finishing cooking it in water would make it watery. In fact, I think I would more worry about the opposite, that it would cook too much of the moisture out of the meat by cooking it directly in water.
Having said that though, if Parksider has done it in the past and has not seen any noticeable deficiency in his finished product I would say it is probably fine to do it that way!