Is Graves in lane viable?

Nope.

Graves can only auto the unit in front of him, So enemy laner can simply play the mouse and the cat in his minion wave. As a result graves will hurt enemy only with his Q ( both Q1 and Q2 damage) and his W which usually it maxes last.

On the other hand enemy can auto behind the minions ( gor melee champions need some practive though) and land all his abilities in theory. So enemy can poke him out of lane more effectively.

Also in order for graves to farm the ranged minions he either has to walk up to them or kill the melee minions or use his abilites and waste mana in the early ( his gonna go oom soon as he wont have blue buff) or let them die.

Overall if the enemy is melee and playing for the 1st time the champion or he game knowledge is not high then yes graves in the hands of an expert can be a viable laner.

if your not diamond, then yes it is.