Okay! Get ready for aicracked question!
This involves the Fey'ri and Tanarukk races specifically. These creatures are considered outsiders, according to their creature type.
HOWEVER...these creatures possess the Elf Blood and Orc Blood traits respectively.
Are they considered persons for the purpose of Spellcasting? For all special abilities and effects, a Fey'ri is considered an elf, and a Tanarukk is considered an Orc.
There's really no good reason to rule either way, except that one of my players kept Enlarge Person on his character's list when we switched our 3.0 game to 3.5, and so I'm ruling in favor of the fact that these two races ARE.
Nothing else is, because the text is clear under 99 percent of all circumstances.
It's just these.
Oh man,
Good question! Unfortunately, I don't have my stuff here in front of me. I say unfortunately because it's not going to stop me from putting in an opinion, it just lowers the validity of said opinion ;-P. Anyway, the fey'ri and tanarukk are planetouched just like genasi, tieflings, and aasimar. As such, they're native outsiders. Period. I would adjudicate that the Elf blood and Orc blood features are meant to be a boon to the bad guys, and not a weakness to be exploited by the PCs. Can a fey'ri become a bladesinger or arcane archer? Yes. Is it subject to spells that don't affect outsiders? No.
I'm sure I'll be taken to task for my stance, but from here at work that's the best I can do for you.
Well, my theory is that it works like every other benefit in the game. A benefit is only a benefit when it is advantageous to you.
Dervish/Power Attack is another screwball rules loophole they never explained, and that's another "Which is it?"
BtB elf blood/orc blood means that they are considered elves or orcs for special effects that affect elves or orc repsectivly (such as Bane Weapons, special magical items that only orcs can use, PrC requirements that require a creature to be an elf or orc etc.)... it does not in any way change thier type which is still Outsider, so enlarge person, charm person etc. would still not affect them.
Are {the Fey'ri and Tanarukk} considered persons for the purpose of Spellcasting?
First off, I don't see how this relates to Paizo's Gamemastery line - the question would have a better home in the D&D General threads.
On to the question. They are 'people,' but they are not 'Humanoids,' which is what you are really asking. The other posters have it correct. As native Outsiders with the elf and orc subtypes, respectively, they are subject to all effects, magical or otherwise, which affect Outsiders and those which specifically affect elves/orcs. They are not subject to any effect that only affects Humanoids or other non-Outsiders.
Enlarge person states that it affects "one Humanoid creature," so going by the rules as written only, your player is out of luck (Though the 3.0 - 3.5 update booklet does specifically mention allowing redoes of skills and spells which are no longer relevant any more).
That's the official answer to your question (though I am not an official source (if that makes sense)). Now then... this question seems like a moot point in this case. You seem to be set on allowing the player continued use of the spell, even though, again RAW, the character in question is an ineligible target. So I gather from this subtext that your real question here is - "will this imbalance my game?".
The answer (from me anyway) is no. I personally see no reason why the enlarge person spell can't affect non-Humanoids. I don't know if I would change it for my game (otherwise I'd have a stack of house rules thicker than the core manuals stacked together), but I would have no problem playing in a game with a less restricted enlarge spell (Even if it means my Medium sized enlarged halfling must now face a horde of Huge enlarged ogres).
Hope this helps,
My 1 sp (keep the change)
TK
cwslyclgh's post is correct: fey'ri and tanarukk are outsiders and are immune to all the things outsiders are immune to. Fey'ri can use items only useable by elves and are vulnerable to things that do extra damage to elves (like elf-bane weapons). Likewise tanarukk and orc items.
This means that a fey'ri could make boots of elvenkind or a cloak of elvenkind, for example (both items have the requirement, "creator must be an elf").