You're welcome.
Oceania is not a new theme, it's a new nation that will likely become available in patch 2.15, which to my understanding is somewhere in the near future as opposed to the distant future.
The units themselves were already in the game pre-2.14, but were not available for recruitment (other than the basic mermen from the merman indie poptype). I made a test-mod where I assigned all of those units to Atlantis and got the info that way. When I discovered that all the merman units had both land-walking and underwater forms, it seriously cut down on the number of actual new units and was just enough for one new nation, whose name we had already heard.
When you look at the ID numbers, the C'tis DT units Tomb Guard and Desert Ranger are all more recent additions than the Oceanians.
Edi