How do +1/6 caster level Favored Class Bonuses interact with the Spirit Vessels Oracle revelation?

Question

While working on a JuJu Oracle for a campaign, I stumbled across an interaction that I wasn't sure how to resolve.

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:

1. 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

2. 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.

Answer 1

Ifrit's FCB doesn't work with Spirit Vessels

The Spirit Vessels revelation doesn't really use your oracle levels to determine it's effects. As you said, it increases the effect of Animate Dead. But not only that, Animate Dead checks your caster level, not your oracle level, which is what is increased by that Favoured Class Bonus.

That FCB will only affect revelations that have a variable effect based on your oracle level and those hardly check for your caster level. Unlike the Dhampir's FCB for wizards, which increases her caster level for necromantic spells and would directly affect the number of controlled undead.

Answer 2

Your first option. Spirit vessels does not use caster level, so changing your caster level for the purposes of spirit vessels accomplishes nothing. To accomplish the second option, you would need spirit vessels to say something like “animate dead uses the caster level of spirit vessels instead of your usual caster level.”

Otherwise, you are treating the bonus to the revelation caster level as a bonus to a spell’s caster level, and that’s a different kind of bonus. As a GM, I might allow it, though I’m not sure that a small bonus to the caster level of a single spell is a great idea.

As it is, just choose a different revelation, or a different FCB. Even if I might allow you to do what you want, I’d encourage you to reconsider it anyway.