For some reason, it sounds like the devs might have missing something on Sammy that lets him be subject to NS. The question is whether he still does his thing as the Ring Bear. As long as he does that, then it shouldn't matter if he was given a career or not. I know other hidden sims like Grim have careers. All you have to do is ask them when you meet them. But I have not seen where NS gave one to them. One thing about Sammy, once you do the ring quest, he will disappear from your game more or less. A new Ring Bear with another name will get created. In my game, I have not seen Sammy again after solving the quest the first time. Idk if he was deleted or is just sitting there in hidden households as I haven't checked.
As for using MCCC to unhide the hidden sims. I have done it but once I looked at them, I exited the save and reloaded so they would remain hidden. Once you unhide them, there is no going back and hiding them again afaik. I view it as one of those just because you can do something, doesn't mean you should do it kind of things. I have no idea what that will do to gameplay going forward and simply won't take the risk of messing up my main save long term by doing it. But that's me. You have to decide for yourself if the risk is worth it.
There is another thing you should be able to do with MCCC instead of unhiding all of the hidden sims, but again, I have no idea what future impact on the save it will have. Nor have I ever tried doing it myself. You should be able to use MCCC to take away the Actor job that the game gave him if you don't like that it happened. Tbh, I wouldn't worry about it and just let things be. At most, one of your played Actor sims might see him at the studio lot when they go to do a gig. Otherwise, you'll probably never know he is in the career gameplaywise. As long as he continues to fill his role as Ring Bear until you solve the ring quest the first time, everything should be ok.
Hope this helps.
