Tested a variety of different mods that add mobs to the ocean and even though OTG's spawn lists include them they do not spawn at all, only vanilla ocean mobs are able to spawn.

If I may add -
They will spawn if the mob is changed from water_creature to any other type however they will spawn in the sky or on land depending which type you define in a custom spawner mod. However, mob mods which add new liquids to the game and use their own liquid (example: Lycnites Mobs - Ooze) will spawn in that mods custom liquid block.

related to #109

Will close this and continue with #109 .