As I understand it Ambient and Ecowitt are both just branded versions of Fine Offset devices which is why they have a lot of compatibility in terms of frequencies and protocol. In fact, I have the GW1000 a bunch of sensors and the Ambient WS2902 array and they work almost seamlessly together. (Almost because the "outdoor temp/humidity" from the WS2902 overrides the measurements from the WH32 so I cannot use that independently). Anyway, looking briefly at the description of the HP3501 it looks like it supports a "user customized website" likely in the same way the GW1000 does, and I suspect is speaks the same protocol. So, my guess is it will very likely work with @snell's driver as is. You might poke around on some of the WeeWx forums or similar and see if you can find anyone who has one who can tell you what the payload looks like and compare it to that of the GW1000. I suspect they are the same and I suspect the driver will work.
I hope this helps. Report back if you get one.