They do it with bare fists, too. I remember at least that royal guard in Crushbone always held that main gauche, and he always shanked me backside. No recollection on others.
What I'm more puzzled of is the damage they do with backstab - in cases like scarelings and abhorrents it seems like backstab does less dmg than their normal melee. EDIT: oop, just got BSed for 260. Hah. =p
http://eqbeastiary.allakhazam.com/search.shtml?id=3768
Folks claiming they backstab up to 100. I've never seen that happen and have played with these guys alot collecting scalps lately. Anyone elses?