I'm not necessarily calling these two counters, but...
Nasus can farm up his Q on ghouls.
TF's passive grants 2 gold per ghoul (doesn't have to be TF in the lane).
These champs turn Yorick's strength, ghoul spam, into a weakness, because they profit from it, when there's usually no advantage to killing ghouls. Do any others?
Trundle's passive will grant him 0.7-2.1% (level 1-15) of Yorick's max health per ghoul that dies, whether he kills it or not (ghouls have 35% of Yorick's health, Decompose heals Trundle for 2-6% of the unit's max health).
Nunu can feast on ghouls. However Consume is his best pushing ability, and if he's blowing it on ghouls, the lane will quickly be pushed against him. Plus, Yorick's sustain negates Nunu's main strength, which is snowball harass.
Does Parrrley give GP bonus gold for executing ghouls?
Veigar can farm up his Q on ghouls. I'd imagine Veigar is a pretty bad matchup against Yorick though. He has a hard time on Dominion.
Anyone with a Tear who doesn't have untargeted spells can farm it up on ghouls. eg. Cass and Karthus can spam their Q without a target, but Ryze can't spam spells without targets, and Soraka needs enemies in range to spam Starcall.