Uhm the western-polish "treaty" was made in spring 1939 after the grab of bohemia-moravia... The poles, in the sight of the west, were a ragtag bunch of unimportant slavs, much as they were in the eyes of the Nazis. The poor right-wing government of the colonels offered the drawbacks of dictatorships without offering its usual advantages, in the west's way of thinking. The only reason they "fought for Danzig" was because it was a convenient place to step in and fight, since the war was now seemingly unavoidable. To think they cared for Poland is a huge mistake.
In fact, in 1938 its HITLER who had a non-agression treaty with the poles. Aside from that, there was the little entente, which proved its ineffectiveness in the sudentenland crisis.
If Hitler had gone for poland first, imo, he'd have gotten away with it, probably would have gotten the 1913 borders on the promise to respect the sovereignty of the rest.
However, he'd need to pull an ace to get both that and the sudentenland later... most likely, it would just be swapping freebies; later down the line, the Czechs would be ready to fight, and the west as well.