There is really no Apple approval to be given or not given here. It is really just creating a new email account. There is no real way that Apple could stop them

There is really no Apple approval to be given or not given here. It is really just creating a new email account. There is no real way that Apple could stop them from doing this if they wanted to. It is up to you if you tell linkedin your email credentials. I would certainly not recommend it, even without their track record.