It's perfectly acceptable! Just as many medicines are toxins, many healing spells could be reworked into something more necromantic in that way; it's said that they only thing that divides the two magics is that one is practiced with the living, and the other practiced with the dead after all. Just let us know if you'd like him to revive a dead person or something else high-leveled as that, since there's something interesting to do with those cases.