In "The Interlopers," how would your reaction to the events in the plot be different if you didn't know what both characters were thinking?
I think you have become somewhat confused about narrative and point of view in regard to this story. We don't actually know what Georg and Ulrich are thinking in this tale. The narrative is told from the omnsicient perspective, as the narrator assumes a god-like role that is external to the action of the story and s/he can look in to the thoughts and motives of all the characters. The narrative is not told in a first-person point of view, which would mean that the narrator is one of the principal characters in the story. As such, we are only given a few glimpses of the thoughts of the main characters. For example, we are told that Ulrich looked at Georg with "something like a throb of pity" before he offered him the wine.
If you meant to ask how our impressions of the characters would have been affected if we knew their thoughts, I actually think the narrative does a very good job of revealing the characters and what they are thinking through their appearance and speech. Their dialogue does a great job of revealing the sudden thawing of the feud between them and their newfound friendship, so I am not too sure if our impressions of these characters would actually be changed if the narration was different.