According to Wikipedia, "In addition, he is known as Kazuma the Treasoner (Torisuna no Kazuma)."
Someone must have taken that to mean it could be used as his last name, even though it's not even supposed to be Japanese... I'd agree he should just be kazuma_(scryed) instead. I've aliased this, though if someone has some information I don't, let me know and we can change it to whatever is best.