How sorcery is threated on Aquilonian society according to wikia :
Sorcery is shunned as the pursuit of evil men
he Dark Templar’s fighting prowess, coupled with unholy spells, makes them a force to be reckoned with.
The Dark Templar is feared throughout Hyboria, with his mastery of armed combat coupled with his mastery of the dark arts. Dark Templars can fulfill two roles, that of a damage dealer and that of a tank. Using black magic to debilitate foes, unholy chants to augment his allies attacks, and spilling the blood of his foes to restore that of himself and his allies. Heroes traveling with a Dark Templar are feared by all, as tales of the unholy power of the Dark Templar travel far and fast.
Sorcery in Conan universe is very dangerous. By that reason, Sorcerers are persecuted in some societies and rules in anthers. In some cases, sorcerers can be considered “gods” like the leader of Hyperborean society
( http://marvunapp.com/Appendix/louhihyb.htm ) or the Khitai emperor god Yah Chieng.
In your oppinion, makes sense that a Aquilonian can use dark magic to enhance his magical capabilities?