V9 and Blue Scarab!I don't agree that attack speed is useless on Atomic GL, since I buy a reasonable amount of AD for the constant melee hits I'm doing, but I think probably V9 is not the best artifact to build on him.
If you want to increase your damage from the passive, stacking health is not bad. And also, it gives you health. Which is important because if you're AtGL you should always be GOING DEEEEEEP!
Edit: That said, Megarod and V9 could be amazing if you're super far ahead and want to give the other team a chance.