Yes, they use can them for spacing I have used similar images in the past trans.gif (a 1 pixel transparent gif file), but the display size is usually greater than 1X1.
1 pixel to align a page wouldn't be noticeable so it would require a larger size 1X25 say, but yes blocking images in Outpost does have an impact, I often see [AD] in place of an image because it matches some of the sizes I have set.
However, a clever designer won't simply have an image imported but will set place holders (the size of the image), so if the image fails to load for any reason the area allocated doesn't collapse.