John,
I don't have a complete answer for you but perhaps you can extrapolate from my experience.
I have a DigiRig which I setup for an Icom IC-706MK2G (PTT = RTS) and I was able to connect to a VARA RMS on 40m and a Packet RMS on 2m with direwolf. This was of course a Windows laptop, not a Pi, so not using pat, but if your Mac can see the Serial Port and the USB PnP Sound Card in the DigiRig, I can't imagine why it would not work with pat.
Danny
K5CG