I don't think the HAT is the culprit, I do not get that error (or any error) running that script on a bare Pi. I tried with 3 different ones now, just to be sure, using a clean but updated Jessie.
I am not sure what the problem is, the main difference I can see between my tests and yours is that your Pi is obviously not the one I'm using. That's not to say I think it's defective, but it's a possibility.
I think we need to summon the whiz @gadgetoid here to shed some light on the error itself... but from what I can tell the init can't assess that PWM is working properly and I can reproduce the error if I target a pin other than 18.