I’ve never heard of anyone using the PWM signal for “Router Enable”. The PWM signal is used, of course, for VFD speed control or laser power modulation. If you wanted to control a “Router Enable” relay via the NC side of an e-stop button, it would likely be better to just use a 5V pin.
As for me, I went with a little external supply connected through my e-stop’s NC side, leaving the router side completely isolated from the Carbide Controller FEED_HOLD side. I figured the potential benefits of total isolation outweighed the additional part. (I do have a laser module on my machine, so I certainly would not have used the PWM pin, of course.)
For completeness, this is how I set it all up: