So, we just did this... was kinda odd checking into a room and not using it at all. The whole point is access to the complimentary express passes that are included with a deluxe Universal resort room.
This past April we had a week at WDW planned out staying on property using my DVC points We wanted to go to Universal for the day and do express pass. Pricing it out.... for a group of four adults, it was less expensive to book the lowest tier room at Royal Pacific, get park tickets as part of the room package and list all 4 adults in the one tiny room (tiny as compared to the 2 bedroom DVC villa we were staying in). We could have listed another person as the max occupancy was five people. Overall we saved 400 or so by doing it this way as just the express passes were so expensive individually just priced on their own.
Staying one night in a deluxe on Universal property gives you unlimited ride express passes for the day of check in and the day of check out., plus early entry if you choose. We purchased one day park to park tickets and had a great time. We parked at the Lowes and walked over.
In reality that room at the Royal pacific would have been way too small and awkward for our party... My husband and I were traveling with our adult daughter and their boyfriend, so all of us were not into sharing a single room for realsies. we already had a bigger more spacious room and did not want to waste time switching for just a single day. So some folks do a ghost room for a single night and the express access but stay elsewhere for the space.