Hi earth,
Not sure if i understand your question. Let my try to answer:
You have NC + OO running on your RPi. The RPi has a single IP address, fx. 192.168.1.62. If you are accessing NC via your browser, you will use the URL http://192.168.1.62/. In your browser you will also edit documents using OO. So it is always the same IP. You will have this IP in the configuration of the ONLYOFFICE app as a service address:
Or are you asking if you can use the “local IP” 127.0.0.1? This would only be possible if you have logged on your RPi, started the browser locally. If you want to use OO in that setup, then you will have to configure the ONLYOFFICE app service address in NC accordingly.
But then you should not be able to use OO from another device - not really sure about that. But you could try this out easily! Change the service address and see if it works!
Curious if your question and my answer fit together 
Cheers,
mbcon