I think essentially this is an AI issue. My lone WoI experience thus far went much as described above: had 3-4 defensive pacts (playing as the French), but the natives only really helped if the REF attacked their settlements (which happened repeatedly, since the AI landed the REF in multiple locations, e.g. in Quebec for a march around the 'Great Lakes' to the RW eastern US where my settlements were). Hadn't tried gifting guns to the natives in this game, as I was busy using guns for other priorities, but that 'should' help. The natives have advantages in the wild, and guns/horses 'should' help them... IF they actually attack the REF when it is out in the open, as a reasonably competent military commander would try to do. However, attacking settlements should be a different story, and the natives should reasonably be disinclined to suicide themselves against overwelming odds.