I don't know exactly what you mean by Wi-Fi based hardware accessory, but yes, they are all separate accessories broadcasting the same SSID.

I have read the technical note, and temporarily joining a network is indeed my use case. My problem is that there's no way (AFAIK) to init a NEHotspotConfiguration (https://developer.apple.com/documentation/networkextension/nehotspotconfiguration) specifying the BSSID, which means that I cannot guarantee that the iOS device will maintain the connection with only one device, without changing to another one with the same SSID.