I don't see why Holo wouldn't allow it. Kson and Coco are
officially unrelated, and Coco graduated on good terms with the company
officially. Why would there be an issue?
Seriously though, there's no benefit in barring talents from playing, it's just stirring old drama and pettiness for no gain. Bad PR no matter how many middle managers Kson pissed off in her time.
Speaking of graduates, I see some Vesties are already suffering from blue dorito withdrawals. Randon hasn't even streamed once yet and there's already dooming about how he isn't the same, poor guy.
Edit:
Randon & Girl_DM collabed just a couple months ago. No reason to assume he wouldn't continue as he was. Just dooming. Vesper & Magni were what defined the Tempus atmosphere, not the Hololive corp they were barely allowed to interact with at all. That's not changing as indies.