I'm not anti-tablet at all.
Far from it: I work with wireless embedded devices daily. What I am against is poorly thought-out UI's where the sentiment is "we'll just use an app for that" with no consideration for whether or not it's a good idea. All other things being equal, I prefer a web interface because it keeps all the control on the device side and anyone with a browser can connect.
Tablets make great user interfaces: they are cheap, easy to replace and highly programmable. But as you mention, the thing they're connecting to can also have issues with discoverability.
If you need to use WiFi to communicate and the device also has Bluetooth or BLE, then perhaps you can use the Advertising Data as a Service Discovery method where you broadcast the IP of the device in the Bluetooth advertising messages. Otherwise, if the device can have its own wireless network, perhaps it can encode its identification in the SSID e.g., "DEV001" and your application can do a network scan for all SSIDs and filter by "DEV"