sure, the common High Ogre and Dryad avoid necromancy, but so does every other race. on average. i could easily see individuals from either race embracing their aversion as a kind of attraction, the way an Arsonist often fears fire, but starts them nonetheless. or, malcontents/pariah could rebel against their cultural inclination and become a Necromancer simply to revenge themselves against those who spurned them. not to mention, there are plenty of learned characters who have decided that Chaos is not only not evil, but beneficial to the Earth - either race could be of such an ilk and work hard to overcome the "bigotry" of their comrades. i'm saying that there's nothing intrinsic to either race (like Biata's inability to buy "Read Magic") which stops them from using Chaos
besides, if Mystics can rationalize the use of Command effects, i see no reason why High Ogres couldn't rationalize the use of Chaos. and, saying either is "playing their race wrong" seems to vie against the vast leniency imposed by most race packets