Didnt test it myself, bcs Paladin feels kinda weird in EA now ...
Cant really say why.
But i heared that if you dont do this:
I stopped the ambush with a successful intimidation roll.
And Goblins are Hostile towards you, you dont break your oath ... but once you resolve encounter with them peacefully, they are concidered "not a threat", if you kill any of them afterwards, its breaking your oath, bcs you just ended life that could have ben spared.
But its just a speculation/rumor ... didnt test it myself.