To get a list of assigned drivers, use the command resource/get_unit_drivers:

svc=resource/get_unit_drivers&params={"unitId":<long>}

{
    <text>:[	/* resource ID */
	{
	    "id":<text>,	/* driver ID*/
	    "nm":<text>,	/* driver name*/
	    "ph":<text>		/* driver phone number*/
	}, ...
    ], ...
}