I don't think Underground Races changed the Common Orc or Greater Orc stats from how they appeared in the RMSR or in RMFRP Character Law. So if you are just looking for the stats, you don't need it. However it does add Scrug, Vard, and Grey Orcs, plus lots of background material and other character options (talents, training packages, etc), so if you want to assess whether the cultural information there can be adapted for your purposes, that would be something to look at. I don't know WoW well enough to answer whether it is close enough to be useful.