I see that PinTool works for Windows and Linux. Does it also happen to work for OSX? Or is there a similar tool that I can use to easily record code coverage for a closed-source app?
Yes, pintool works on os x as well (Snow Leopard or newer for the current tech preview ver).
Yes, they work as @broadway already pointed out. However, PIN under OSX have many-many restrictions, some of them documented and others not. The most noticeable feature it lacks is support for creating threads in a PIN tool.