This is a good idea. Perhaps enemies could use a line from their friendly speechbank instead of their hostile speechbank until they notice you're an enemy.
Elves would of course be less gullible to this, because idk elfy stuff i guess.
Half-Trolls should be quite hard to fool. Not because they're smart. Because they're huge.
Dwarves should also be less susceptible to this, because (1) They are much taller (2) "You need to work on that beard, player!"
Men would be the most easily fooled. Because you're a Man, they're Men. Rangers would be as hard to fool as Elves though, because they're Rangers i guess.
Hobbits would be unaffected, because:
1 - They are suspicious of Big People.
2 - They don't have faction armour.