The NPC Hozan compares adventurers to ronin (something about how adventurers serve no master) Unfortunately, I can't revisit to give you his exact words, since the NPCs change their dialogue or disappear as you progress through MSQ.
As far as I know, there are no NPCs claiming to be samurai. Hozan's father might have been? But he could very well have been a ninja like his son too. (Just speculating, since NIN AF was plate/chain, maybe the scale armor awarded to him in the past was a samurai's armor. There's no way of knowing either way right now, but I hope there's more to hear from this family in the future.)
In short, they're hinted at but there's no lore or known samurai NPCs.
As far as I know, there are no NPCs claiming to be samurai. Hozan's father might have been? But he could very well have been a ninja like his son too. (Just speculating, since NIN AF was plate/chain, maybe the scale armor awarded to him in the past was a samurai's armor. There's no way of knowing either way right now, but I hope there's more to hear from this family in the future.)
In short, they're hinted at but there's no lore or known samurai NPCs.