I ran into some Rieklings outside Thirsk Mead Hall, who then made me speak to their tribe leader. 3 small quests later and I've defeated a bunch of Nords for them (who I assume were planning to move into their Mead Hall).

My question is, if I avoided Thirsk Mead Hall and went to the Nord camp nearby, could I have sided with the Nords and took the hall back?

Yes, you've pretty much summed it up. It depends who you speak to first. Although, I sided with the Nords, and after some of the choices I made during their quest they're not especially friendly now.

Yes however in my personal opinion (Being a nord myself even) they're a bunch of tools, wish i helped the tribe!

This. Definitely this.

Thanks everyone. Glad I sided with the Rieklings then. I enjoyed beating those nords to a pulp

just out of interest does helping them change the disposition of reiklings towards you? Is it like a forsworn thing where even if you help their leader only about 5 of them are friendly