Depends on how you'd define it, I think. If you think of this as a My Little Pony fan fiction, then yes, Anywhere but Here is a fully OC story. However, if you think of it as a Fallout: Equestria fan fiction, then it's not because it includes FO:E characters.
I've only read the first couple chapters. Not my cup of tea overall but maybe I can shed some light. The chick's name is Paharita, and Double Tap's pretty much her pet. He's a big goofball - put it this way. You know the type of videogamer who just charges in, no caution, kick's ass because he's so good? Tap is that kind of player's character, but you get the sense that he's not really capable of getting himself fed, clothed, housed, or laid. That's okay 'cuz 'Rita takes care of those little details for him.
She's the sweetest little psycho merc ever.
At launch the authors promised FoE but with less talking, more shooting, less navel-gazing, more mayhem. The first chapter certainly delivers. Tap's getting drunk out of his mind and blacking out - but the story's from his perspective. If you read between the lines and 'Rita hitting him up for feisty sex (yeah, it's one of *those* stories, but well-written) you realize that also negotiating a contract, which at the end of the chapter you learn is to assassinate - oopsie. Spoiler!
I stuck with it for a while, but things get kinda experimental with the narration. (I *guess* Tap starts savescumming, maybe??? If so, that's a really clever breaking of the fourth wall, but I can't put up with that for a whole novel.)
But, yeah, I can totally see Tap agree to the whole hoof-painting thing. Because best sex ever makes it worth it. Adorable art, by the way. This is exactly why I love the pony fandom - even our darker-n-edgier lemon has the cutest spin-offs.