There is no evidence that those people are real.
Most likely they are ghosts or tricks of artificial intelligence.
But seriously, there are links to profiles to linkedin (some of them). Guess you could ask them personally.
I mean is there any proof by a third party. for example there are several guys from mycelium but I could'nt find them on the mycelium website
So far, I can not understand what do you mean. Like there's a photo on the Microsoft webpage with the link beneath it to IBM website where they say "hey, this guy really works there"?
We'd love an example how people solve the "fake linked account" problem.