Not necessarily. You can't be 2 vtubers at once if it will conflict or cause conflict of interests, but people still do PL/IRL stuff while in Niji, many just chose not to because that was the MO of all vtubers going into corpos in the earlier days. Exception being Mel and Noel still deep throating their mic on the side. Pomu had the ability to do things as Mint if she wanted to but she used it as a journal. Selen did her art stuff on Doki (mainly for clients ghosted when she became selen) and (in)famously, Hana getting pounded by her (Dad) on the side are all fine. I think like Hololive it's more of a case by case situation, something Sayu leaked in her original document.
Twisty situation is probably toeing a hardline of what she shouldn't do as she'll be collabing, but at the same time she's pretty much shitcanned so she may as well do it. NDA is funny like that because Niji is also held to NDA so they can't call out her behavior directly either because they don't control the personal lives so as far as anyone is in the know, she's just on hiatus.