Thanks again for your suggestions on this.
I would happy to use regular sprites, but the arrows are skewed to isometric angles and need to resizable, set to any random size in the layout, which is why the arrow bodies are made using 9-patch and tiled background objects (the arrowheads need to stay at fixed dimensions). AFAIK, there's no way to stretch a sprite (besides a simple line) along one axis without distorting it, is there?
The use of containers makes it easier to treat each arrow as a single object in the layout. Sure, I could manage all the resizing/aligning behavior in code at runtime, but that means I'd have to build an entire editing system that saves and reads in all the arrow/object sizes and positions from external files, a fairly non-trivial amount of work.
Anyway, I was also looking at using scene graphs as an option, so I guess I'll give that a try.