Ok, so the "definitive answer" part might have partially been due to my being up waaaaaay past my bed time, but here's the evidence which still has me convinced.
He was youthfully scrawny, his skin bronze enough to look Native American, though his tangled red hair and pug nose argued otherwise. His eyes were an odd shade of brown, so light as to be nearly golden.
Ok first bronze skin on a redhead is really unusual. ESPECIALLY in a snow storm. Redheads typically have fair skin. When they get a lot of sun they get freckles on top of freckles. So the Redhead and bronze skin are off, and are probably from the 2 different sides of the family.
But here's the clincher.
I broke out into a cold sweat and looked out the other window.
Directly into a pair of brilliant, feral, amber eyes.
...
"I am Harley MacFinn's fiance. Miss West," she said. "I am called Tera."
Tera West was there, [/snip]
She was naked, her body a uniform shade of brown
Also, after mentioning how Father Forthill could sense Harry and Stuart because the good priests, ministers, shaman's can sense spirits Stuart says:
"And dogs." Sir Stuart added. "Maybe one in ten of them seem to have a talent for sensing us. Probably why they are always barking."
So if he is half wolf=>human shape-shifter, that might help explain why he can hear spirits.
Finally we have this.
“I seem to remember at a Q&A a few years ago, you said Tera West would be showing up in Book 13 aka Ghost Story. Is this still happening, or has her character been shuffled down the line a bit due to the change in total number of case file books?”
My first answer is “bump her down a couple.” But on the other hand, it might be interesting to see her again in this book.
We’ll see what happens. 
I think she showed up in proxy too, as in not her, but as the mother of a new main character.
I believe Tera West is the only other character described with golden colored eyes, she had bronze colored hair, she was a Wolf, thus likely to have progeny that sense sprits, and she was the Fiancee of an Irishman she never married.
Sounds like all the pieces you need to put together a young man described in the first quote.
The only off part is the timeline. I believe FM was around 12 years before GS, which means that either Fitz was already around somewhere, or he aged quickly (dog years).
