Usually when the game refers to armor (like armor sets) it doesn't mean shields just helm, chest armor, gauntlets and boots perks like matching set don't need a matching sheild for example (but the unofficial patch does tag Spellbreaker as Dwarven anyway).
I can't seem to find a yes or no to if Ancient Knowledge effects shields though (the perk juggernaut doesn't), you may have to do the math to know for sure but the shield shouldn't negate it.
Thank you, it does seem that Ancient Knowledge effects my shield since I had been holding a dragonplate shield and the Dwarven shield caused an increase in the overall armour rating. And a little green +# when I highlighted it.
As for Spellbreaker, the base shield (without smithing) does show a in raise the armour rating when I highlight it in the inventory, even higher than the Legendary Dwarven Sheild I had been using. So whether it's becuase of Ancient Knowledge or just because it's a powerful shield, it doesn't seem to matter anyway.