No problem. Unholy gives you a few great abilities (ESPECIALLY if you're using shamans/mages for DPS). First you get reduced cooldown on death and decay which does a LOT of aoe damage and generates a ton of threat. Second, you get the 51 pt talent unholy blight which also does a lot of damage AoE and generates a ton of threat. Combine that with increased pestilence damage (AoE as well), increased blood boil damage (AoE), and things like anti-magic zone and you have the perfect AoE/multiboxer tank. The ghoul pet is just a side bonus

Last, ebon plague being spread to all mobs means they all take 12% more magic damage (gogo chain lightning!)