For that Itinerary your *Gold card would get you into the Business or Senator Lounges, but you would need to be flying in First Class to access the First Class Lounge.

So let's have another example here. Let's say you were a UA *Gold who booked a flight from ORD-NRT on NH and were crediting those miles to OZ. You would be able to use the SK lounge in Terminal 5 even if you were in economy class because you are *Gold. You would also be able to access any of the various United Clubs (NOT the GlobalFirst Lounge though) since you are a MileagePlus Premier Gold member who is flying on an international flight.

One more example: If you were a UA *Gold member flying from IAD-LAX you would be able to access LH Lounges (both Business and Senator) but you would NOT be able to access the United Club even if you were flying in First Class because United does not let their own *Gold passengers in their lounges on domestic itineraries. This is something that I believe is unique to UA (Reasons being the vast amount of passengers they handle as well as them selling memberships to their clubs.), and a Gold member from any other *A airline would be able to access the United Club.