I ended calling Universal guest relations, they said the hotels wouldn't accept bags from non guests.
However, I did find a solution!
Lost and Found at either park will actually store luggage. I don't know what their limit is, but they took my carry-on suitcase no problem and even offered to store my backpack. However, it's not like a locker where you can keep going to it throughout the day. Once you check it out it's checked out.
Felt weird rolling it through CityWalk, but it was a super convenient service and didn't cost a thing