The phrase "as their driver" is correct and usable in written English.
It can be used to indicate that someone is serving in the role of a driver for a specific group or individuals.
Example: "The team relied on Sarah as their driver during the long road trip to the conference."
Alternatives: "in the role of their driver" or "serving as their driver".
They have heard that the guru, a bit of a smart aleck, can do wonders, but he has only an hour, as their driver is waiting.
On a trip to a Mormon congregation in southern France, President Anderson, as he was known, and his wife, Leola, who was called Sister Anderson, took Mr. Romney as their driver, and another young missionary, David L. Wood.
His other film credits include the British action thriller Collide, in which he portrayed an American backpacker who becomes involved with drug smugglers after getting a job as their driver.
Ward's kid brother, Jack (Zac Efron), a college dropout with nothing to do but lounge around in his underwear, is hired as their driver, and instantly becomes sexually obsessed with Charlotte – to her open amusement.
In an ambivalent role, the Oscar-nominated Mortensen is outstanding in an intriguing, but unbalanced film, with midwife Naomi Watts and her home life providing an underwhelming counterpoint to the far more compelling affairs of Russian restaurateur and underworld boss Armin Muller-Stahl, his loose cannon son (the versatile Vincent Cassel) and Mortensen as their driver.
Sauber had been expected to run the Russian teenager Sergey Sirotkin as their driver following an investment deal with a group of companies from that country.
TV lights flickered through the windshields of some cabs, as their drivers reclined on their bunks.
A doorman tells me that he has seen horses break lose and gallop across Central Park South late at night as their drivers were packing up for the day.
As their drivers are sealed ever more inaccessibly into a casing of audiotapes, cell phones, and deafening air-conditioning, automobiles for the sake of their own survival are evolving increasingly complex speech patterns.
The pack of dirt racers slid into and out of the four turns on the clay oval, whining in protest as their drivers stomped their gas pedals when they hit the short straightaway.
Officially, Caterham have retained Finn Heikki Kovalainen and Italian Jarno Trulli as their drivers.
