What website do you learn these things from?

 

http://minecraft.gamepedia.com/Minecraft_Wiki

And per the site yes they can spawn/happen. However its a matter of the plugins at this point.
The server has Essentials and World Guard plugins that you can turn on and off spawning of any or all mobs.

So even if you kept restarting your island till you got an ocean biome, you would have to /fly to find out if the center of the ocean biome is inside the island boundary.

 

You can use a monument chunk finder to find the exact locations where these guardians will spawn. They are VERY far apart though.

 

There is an alogorithm to it, as @Halex00 mentioned earlier.

 

Algorithm*

 

Haha, thanks