I have three characters at endgame now so I've done that section with each of them, and I only remember getting caught by the statues once - not sure if it was my fault or an NPC, but it's clearly doable without being caught at all.

Or to look at it another way, if you the almighty Warrior of Light can be caught out, why shouldn't they?

(Though I would have assumed the NPCs are immune to being spotted in those situations so long as you're doing it right yourself.)