I think the bigger factor to consider here is that blacklisting (either formal shared blacklists between industry peers, or informal gossip-turned-policy situations, which are likely much more common) have no moral motivation despite being framed as such, and instead exist for a) assumed PR risks, and b) convenience.
To use Sayu as an example, I doubt the big players who refuse to associate with her are actually upset by the things she's said and done (since anyone with a functional brain can see a mile off that she's harmless) - but they don't want to deal with the baggage that comes from working with her. They do not want every post about the event they invite her to to be drowned by 16-year-olds "voicing concerns" about her edgy jokes. They do not want to open their email every morning to another """journalist""" asking them for comment about the latest Nijisanji controversy that's been manufactured for views. They do not want tourists showing up to their stream chats, trying to bait them into taking a hard stance on her drama. These are the kinds of things that people are probably warning each other about behind-the-scenes, that result in a kind of unwritten blacklist.
I don't know exactly how this would apply to something like Hololive since I'd assume they're big enough for whiny twitter nonsense to bounce off them, but the vtuber orbiter influencers are much more prominent now than they were a few years ago. If Mori were currently an indie vtuber then a bunch of the normie fleshtubers who're two degrees of separation at most from Ollie and Flayon would probably have already made videos and tweets calling her racist; I don't know if Cover'd care that much about it, but I'd guarantee they'd pay more attention in that situation than back in 2020 when her loudest detractors were just weird anons. At the very least, I could see "someone warned me about this person" being the tiebreaker between two equally-fitting candidates during talent recruitment, which, while not technically a blacklist, still involves someone being disadvantaged because others around them created smoke where there is no fire.