The answer is still the same, defense bonus doesn't apply to animals. Only defensive units benefit from the bonuses. (at least if there isn't some recent bug with them)
You can check this easily from clicking on the oasis and looking at the upper right corner.
Pictured above is a iron mine which has 0% bonus because it's under animal control but if you were to capture it it would change to a 100% like this
The bonuses listed by Georgi should also be correct
Interesting... so is defending an iron mine better than a level 20 gaul wall + level 20 water ditch?
Yes + it can't lose the bonus like a village could thanks to rams. If you can bait people into attacking an iron oasis then just defend with everything because that's the best fight you can ever get.
That being said for somewhat obvious reasons people don't often attack oasis with full force so it's rare to get to use their defense bonus to your advantage.
What is perhaps more notable is that crop oasis (without other resources) have 0% defense bonus making them perfect targets for cavalry hits
