As a GM, I would allow it, and have done so. I actually pointed it out to the player who was building a Lunar Oracle.
There are plenty of much more potent combinations, and I don't expect it would hog the spotlight in a well built party. Obviously an optimized character in an unoptimized party will outshine the rest. And also obviously, a well built Tier 2 character will outshine a poorly built Tier 4 character.
We had a mounted lance-wielding cavalier, who managed a charge almost every round (not a dungeon crawling campaign, so charging comes up more), and a Synthesist, and an Inquisitor, and a couple other charaters I don't recall at the moment (Party of 5). The one who hit hardest was by far the Cavalier. Admittedly, the game only went up to level 5 (that was when I got Edge of the Empire, and wanted to try running that instead)
I found the Cavalier a little frustrating (he could one-shot most opponents, and was raely in range to get hit back), but the Oracle Tiger wasn't that big of a deal.
Plus, Animal Companions start to lag after level 8-10 or so anyways, and you still cap out at a 15HD AC, you just do so earlier.
And RAW, it works (I don't play PFS, so I won't speak to that, but PFS has all sorts of limitations on top of RAW).