In my understanding, if such a clause exists, Microsoft employees should not solicit OpenAI employees. But, there’s nothing to stop an OpenAI employee from reaching out to Sam and saying “Hey, do you have room for me at Microsoft?” and then answering yes.
Or, Microsoft could open up a couple hundred job reqs based on the team structure Sam used at OpenAI and his old employees could apply that way.
But it wouldn’t be advisable for Sam to send an Email directly to those individuals asking him to join him at Microsoft (if this provision exists).
But maybe he queued everything up prior to joining Microsoft when he was able to solicit them to join a future team.