I'm starting to think that there might be a possible re-evaluation of the "hill-men" of Rhudaur, along the lines of the late redefinition of the Dunlandings as descendants of the House of Haleth. The distance between Bree and Rhudaur isn't that much so couldn't these hill-men have been kin to the Dunlandings (and Bree-folk)? In that light, as the Dundlandings turned to Sauron for protection against the Númenoreans who were devastating their lands (the enemy of my enemy is my ally), these indigenous hill-men might have sought the 'protection' of Angmar against the Dúnedain outlanders.
What do you think?

:This is perhaps why the Dunedain's population was so wiped out when Fornost and Annuminas fell, because most all the Dunedain of Arnor gathered near those cities, and when they were sacked, most of the people died.

Good point. I had never thought about it that way. I'd always assumed that the Dúnedain of Cardolan had become the forefathers of the Rangers who centuries later recognized Aranarth (Arvedui's son) as their legitimate lord, i.e. their first official chieftain.

Thanks for your ideas