I have used FTDI based USB to serial devices, and they do not require drivers on recent Macs like yours. In other words plug them in, and they should just work. I recommend that you do not attempt to install drivers since not only should they be unnecessary, they will almost certainly be difficult to install (and prove just as difficult to uninstall).
Macs don't use "com ports" but their Unix-like operating system will automatically add the FTDI device to one of its many devices in /dev which you can peruse to confirm it appears:
ls /dev
For example, connecting an Arduino board to the Mac automatically adds the device named tty.usbmodem14101 and connecting an FTDI device adds a device named **.serial
Those are both serial devices, and those names are merely examples.
I don't know anything about RTSystems cables, but if they use the FTDI chipset they ought to be the same.