Does anyone know if Yagak gro-Gluk(the orc in craftmans hall by Bols Indolen)has any importance to any quests? Even quest that aren't main quest or faction quests? I want to taunt then kill him for admantium since I cant taunt the Imperial guy in Ebonhart and since I think he may still have an importance after I can reach Mournhold(even though he probably does not). But anyways, back to the point, does Yagak have any purpose?

There are better/easier ways to get adamantium armour than killing. Install the official adamantium plugin by bethesda, then rob the wood elf armour-smith in Balmora. He has a chest full of adamantium armour in his bedroom downstairs.

Yes. You will not be able to complete the main quest if you kill him. Go and get the ore from the sewers and have them make adamantium armour for you. There are quite a few pieces lying around in the sewers anyway.