Hiring is always the producer's call, a cinematographer can only recommend. However, if a producer is entrusting the cinematography to someone, it would be odd to ignore the cinematographer's opinions on things that affect the cinematography -- like the crew that gets hired. Assembling the camera, grip, and electric crew (or at least the keys) is a normal part of a cinematographer's job duties.
On the other hand, there are always financial and logistical considerations that will come into play that may take some of that decision-making out of the cinematographer's hands, depending on the budget and the nature of the production. I did some low-budget features where the gaffer normally worked with that producer (no matter who the cinematographer was) because he had a deal on electric gear, and I've done a few shows where the producer wanted me to hire a particular key grip because of the deal on their truck package. It happens. Of course, generally the producer isn't going to push someone incompetent on me because that will only hurt the producer's bottom line in the end.
I remember once having to hire a family friend of the producer's on a show and I struggled with the skill level of that person until a few weeks later the same producer asked me why I hadn't replaced that guy!