If I play as a Ifrit (or Elf, or other race with the same Favored Class Bonus) I can take the bonus of
Oracle: Add +1/6 to the oracle’s level for the purpose of determining the effects of one revelation.
One of the Juju revelations is Sprit Vessels
Spirit Vessels (Su): You can channel wendo spirits into lifeless bodies, reanimating them to aid you. When using the animate dead spell, you can control 6 HD worth of undead creatures per caster level rather than 4 HD. In addition, any zombies or juju zombies you create using animate dead, create undead, or similar spells possess maximum hit points.
If I take my favored class bonus of +1/6 caster level to Spirit Vessels, what actually happens? I see two options:
Nothing happens, it's a waste of a FCB. This is because Spirit Vessels doesn't actually check your caster level itself, it just alters the wording on something else, which does check caster level
Every 6 levels, I gain an extra 6HD of zombie minions. This is because Spirit Vessels replaces both the number of HD of contollable minions and checks the caster level itself.
A good answer will provide sources (errata, similar scenarios, or actual clarifying rules text) for your answers, as I can see either argument being supported but have not found anything definitive myself.