What is the departure point. If in DXB, no issues, just book the one car and he will hop on. At outstations they can sometimes get a bit iffy with insurance and some other nonsense, so I would just put a note on the booking.
Agree in DXB its fine, I even got the driver to drop my gf off at work once on the way to the airport! (She had been waiting outside for ten mins trying to get a cab first so not as bad as it sounds, and its right on the way to the airport!!)
In the UK I had an issue once with a driver who didn't want to allow my colleague to get in the car (he was in Y same flight) but in the end it was allowed.