I believe the Universal Devices ISY994i must utilize an Insteon (serial) PLM. In this sense, the Universal Devices ISY994i is functioning as your home automation controller, similar to openHAB It appears that you can use the ISY994 with openHAB directly though as there seems to be an ISY binding.
The binding may be a openHAB v1 binding which will eventually be incompatible with openHAB3 (when it is released)
A simpler (and cheaper) solution would be to use the Insteon USB PLM and the Insteon binding.
The above binding is a native openHAB2 binding and will be compatible with openHAB3 (when it is released).
For the price of the ISY994i, you can add a lot more home automation via openHAB. The only trade off may be that you will need to work a bit (and invest time) to get things working as you’d like by foregoing the ISY994i
I have also in the past used the Insteon Hub, but all that being said what you cannot do with the Insteon binding itself is configure your devices and/or create Insteon scenes. You will need 3rd party software to do this and since the 3rd party software will require use of the same PLM, you’ll have to shut down your openHAB Insteon binding to do this (although this is quite rare, it is still a PITA). People who use the ISY device and binding report that the ISY has an interface unrelated to OH in which you can configure all devices and scenes directly without any other software.
I use https://github.com/pfrommerd/insteon-terminal to configure hardware and manage scenes, but this has some learning curve to it. Other people use the (now ancient and unmaintained) Insteon Active Home Windows software, by unplugging their PLM from whatever device they run OH on and temporary connecting it to a Windows Box.
I’ve never tried this one either, but have considered it. This runs separate from OH but can be connected to OH via MQTT, which if you do not know, is a very universal databus for smarthome automation. This bridge is reported to also have built in device and scene configuration as well.