Given how much the Northern mountain clans hate the Boltons, and their fierce loyalty to the Starks, do you think it’s odd that they were just chilling in the mountains until Stannis recruits them?

Not really. The hill clans also have a strong belief that, if they’re going to set foot outside their hills, you need to come and ask them in person. And with Winterfell completely discombobulated in the wake of Theon’s sneak attack, no one ever asked for their help.

That being said, there is that one Liddle…