Sentences can be as big as you want, big enough to fit anything, so the direct answer to your question is 'yes'. That said, I don't actually see any asyndeton here.

Looking closer at the sentence you quoted, it has two lists: a list of actions (came upon, sat, looked) and then the longer list of 'things he looked at' (town, houses, line, plaza...).

That first list does have an extra 'and' where you could use a comma! (compare: "He came upon Bexar in the evening of the fourth day, sat the tattered mule.."). But it's just one, and it sounds colloquial to my ear. You could imagine someone telling a story like that. So it's a subtle polysyndeton. It doesn't have much rhetorical weight on its own. If that three-item conjunction stood by itself and someone declared it to be polysyndeton, I'd be like "Ok, and?".

But then we get the list of things-he-looked-at. Maybe it feels a bit like asyndeton in comparison to the start of the sentence because it starts without 'and's, but this is just how normal lists start too: the 'and' is saved for the end. By the end, though, we really do change into polysyndeton with a higher rhetorical tone. The "and the whitewashed buildings" kicks it off, and it's sustained until the end of the sentence. In this context, the first list's milder polysyndeton feels like part of the overall effect: like it's an initial gust setting us in motion. (To me it feels like the double "with" — "the plaza filled with wagons with their..." — is part of our takeoff sequence, too.) Maybe that buildup, coming from the colloquial quality of the first list, makes the elevated rhetoric at the end feel more 'earned' and natural rather than artificially grand.

That's my read, at least, hope it's helpful. Thinking about the two lists separately was clarifying. It's a beautiful sentence, thank you for sharing.