I bet it'd be pretty easy to make it work using a RaspberryPi's on board wifi and an ethernet cable to the router.

Dual wifi makes for easier installation/operation in a lot of situations though, so I think its a good "default config". If there's already a wifi network people can use, hooking one wifi chipset to that then connecting the phones under test to an access point broadcast by the other - is easier than expecting there to be a live ethernet port and someone at a womens shelter-style-place having access to it and skills to use it.