You could and you should allow that. Why not? The risks of casting a spell every round are significant, and a Complication that is rolled could be that you lost control over the already re-animated undead and they are now uncontrolled, bound to kill the sorcerer. That is what Complications are for.
If a sorcerer PC casts this spell in three consecutive rounds, he or she cannot leave the current zone, if they spend the Minor Action to prepare the spell, else they would cast at +1 Difficulty.
That means they are a stationary target for everyone who, after the very first spell, knows they are sorcerers.
And engaging in obvious spell casting, that makes it clear - even for your party members! - that your are one of those evil, depraved, untrustworthy, traitorous, backstabbing, friend and family sacrificing sorcerers! - And other PCs might react on that accordingly.
“Normal” Sorcerers in a Conan PC group are usually of untrustworthy reputation - well deservedly. But a Necromancer? What kind of Hyborian hero would associate themselves with those, other evil, depraved, morally corrupt sorcerers look down upon, because even they cannot bear the atrocious, blasphemous way necromancers abuse their powers?
Of course, your player group might be well OK with playing the “abysmally evil” group of non-heroes, then this kind of re-animating the fallen foes and making their comrades fight the bodies of their friends, brothers, sisters, spouses, might be alright with them.
And that would lead to a much more efficient way of using the sorcery skill:
Don’t cast Sorcery every round to re-animate some puny minions. Re-animate a few, then, next round, use the Display of Sorcerous Might on the group of foes.
5[CD] plus Personality bonus damage at Medium Range, Area quality, Intense quality!
That will take out more opponents in a single action than dozens of minion-type NPC undead might be able to.