Client must advertise itself as supporting a known controller model, and then map into that model.
There have been some discussions of how to be more forward-compatible with new devices with their own controllers, but haven’t yet come up with a solution or a timeline.
For the HP Motion Controllers, my quick first take would be to map them as oculus touch controllers. The menu, grip, and trigger should all map decently. If it’s the model with the touchpad, you’d look to interpret the touchpad as if a dpad, and have left/right generate a/b (or x/y). If it has abxy already, just send those along like touch would. In steamvr, anywhere it renders the model it will render the touch controller, but that should still be much closer than the vive wand in my quick view.