Hmm. The first thing to check would be to verify that you are running the tool as "root". When running the recovery command on your Mac, are you being asked for your password? The program needs direct access to USB devices to talk to the camera, hence the password request. (If you are running the tool several times in a row, you may only be prompted for the password the first time, which is fine).
Next, I would make sure that you are following the recovery steps correctly. That is, remove battery from camera, hold down the Record button (top), plug in USB, then let go of the button.
Next, we could try to play with USB a little. Unfortunately, the USB recovery mode built into the camera is a bit quirky, and it might not work with all USB ports. For instance, I get the same problem on my laptop when I use a USB 3.0 port, but not a USB 2.0 port (but my other laptop only has USB 3.0 ports and they all work fine). So as you can see, it's a combination of USB quirks in the camera's bootloader, and how computers respond to those quirks. With Macs, sometimes it helps to insert a USB hub between the camera and the Mac, though on other Macs, I've seen USB hubs cause problems (and plugging the camera directly into the Mac).
Next, and I realize this may not be particularly helpful, you can ask around and see if you know anyone with a PC, to see if things behave differently. I know this is a bit of a cop-out solution, but hopefully the recovery procedure is only something you only have to do once.
Finally, it is possible that the camera is electrically dead, which might explain why it won't enumerate over USB. My tool can only recover firmware-related issues (mainly caused by glitched updates), but there may be other reasons a camera could be dead (such as something being shorted or fried) which would require physical electrical repair. In your case, I am not sure what the problem would be, but it IS entirely possible that the failure to detect the camera is caused by Mac OS quirks, rather than by camera damage. But you never know (which is why comparing to a Windows or Linux PC might be interesting). As a wild guess, if your camera was bricked by a failed update installation, there is an excellent chance you will be able to recover it. But if the camera was bricked by falling into water (especially salt water), then that's obviously a very different story :)
Good luck, and sorry I couldn't be of more help here
Ps. Hero4s in rough environments can in rare-ish cases develop corrosion in the Herobus port, which can sometimes short out the power/ground signals and prevent the camera from turning on. If you know this is the problem, cleaning the corrosion out of the Herobus connector with a little bit of alcohol can help.