The Question and Answer section for The Interlopers is a great resource to ask questions, find answers, and discuss the novel.
Ulrich von Gradwitz is unable to shoot his enemy because he subscribed to the "code of a restraining civilization." This code prohibits shootinga neighbor without warning or words exchanged. This does not count in cases of family honour.
Yes, in the end, Georg and Ulrich do become friends. Stuck in a place where neither man can get free or take advantage of the other, they are afforded the opportunity to talk and settle the feud between themselves.
In the end, Georg and Ulrich note the arrival of a pack of wolves.... we are left to guess at the result.