Hello Marshall.
I would rephrase your statement - how, using ARDUINO board with
AR9331 CPU for routers, run Opener.
I would say that you need to biild image with linux and embedded OpeNer.
AS quriousity I tried to find some info about such CPU but on website there no any software to build image, may be i didn't look well but may be someone will find.
I ported Opener to cortex M7 and M4 as for me works fine, even found bug in STM software with that stack, didn't even expectedto get it.