Yes, the Zaurus and most iPaqs have ARM processors, too, but you probably can't just copy over the binaries (the NIT is a generation or two newer, both hardware and OS/software-wise). The fact that people got GRASS running on those machines is encouraging, though, I would have presumed it is harder to do than QGis (GRASS has a lot more dependencies, and IMO more exotic ones, too - like opengl stuff, the TK ui, etc). GRASS also has a bit of different focus compared to QGis, QGis is more of a very fancy GIS data viewer, GRASS is oriented toward analysis, obviously with some overlap in functionality between the two.

If you just want (not too large) shapefiles on top of WMS layers, I'd suggest going QGis. In fact, as Maemo is turning to Qt winds more and more now, the chances of QGis appearing in a repo are actually pretty good. Also, Qt will make your life easier with it's build system (unless you're an automake pro, of course).