Well, I said in another thread that I'm translating things from bGC (brazilian GC), so some of them should be inacurrate, Ntreev will probably use other names.
And yes, he's a ninja. In bGC he's a ninja, the translation from the old jGC is ninja.
Otherwise, he's a thief like you said. Actually, that would fit a lot better, since his 4th job (Evan Stripper) wears a katana. Ninjas were the enemies of samurais, so...
Thanks for your help. :3