Grid 2 RE for Mac doesn’t recognize PS4 controller

There are a couple of drivers out there that allow you to use an xbox controller on a mac, for example http://tattiebogle.net/index.php/ProjectRoot/Xbox360Controller/OsxDriver. Wired controllers can just be plugged into a usb port, but to use a wireless controller, you need an Xbox 360 Wireless Gaming Receiver.

I'm still interested in the real answer to this question, but in the end, I just found a controller that works.

For anyone else who really wants to do this, keep trying different controllers until you find one that works. I recommend quality console controllers (gamecube, PS2, xbox) if you already have them, connected using USB adapters, or cheap USB gamepads from eBay.

The one that worked for me cost about $7 (bought from wholesaler xinga.com years ago but try ebay etc). It's a semi-transparent (purple) chinese knock-off of the standard PlayStation 2 dualshock controller. Windows recognises it as "PS converter", so the electronics are probably identical to USB PlayStation 2 controller adapters sold by the same company (and many/most other companies, probably).