You are confusing two things.
1)Escorts can ask for photo ID, I don't like it but I suppose it could be justified under "safety/security concerns" maybe for outcalls etc...
2)The LinkedIn verification / or "email sent from your employer's address" is "employment verification" basically it's a way they screen people out through social class. So CEO - yes, checkout worker at Tesco's - Not so much. It's not enough to turn up with the money, they want to make sure you are of the correct social standing before you blow a load on her face.
The 2nd practice is commonplace in the USA and has been imported over here and is now increasing prevalent especially in London. What they do is conflate the 2 practices and pretend it's about "safety" because they don't want to admit to the 2nd practice because it contradicts much of their LARPing as bleeding heart/save the world types.