I don't think any of them have their own staff airside; they subcontract to a vendor which provides the services -- the same one that airlines use for VIP/CIP.

A few years ago, I arrived into HKG in first class on TG and had arranged for the meet and greet service from the Landmark MO. I got to the end of the jetbridge and found two people with name placards and buggies waiting for me; pretty sure they were from the same outfit.