I think I know the answer to this, but thought I'd pop it out there anyways. Does the caster level that creatures with spell-like abilities have stack with any spellcasting caster level they might also have?
From the Bestiary, page 297, on creature advancement by adding class levels:
If the creature possesses class features (such as spellcasting or sneak attack) for the class that is being added, these abilities stack.
However, the Bestiary does not mention how Spell-Like abilities are affected, and states that creatures with (Sp) are not treated as "spellcasting creatures" for the purposes of determining the type of role they fall into.
Spell-Like abilities do not stack. Just actual spellcasting the creature may possess.
That's what I thought, thanks!