How, precisely, would you stat John's gift? Which, by the way, not only allows him to find anything, but to kill anything (up to and including deities) as well. More or less instantly. And has been with him since his first appearance. Or his bullet-stealing trick? I could likely manage the second, but the first is...difficult. You could probably do something with the Sword of the Cross's "I Am Your Catch" as a basis...but it's still going to be really expensive to buy as an ability. Even one costing Mental Stress. And very jury-rigged to say the least.
But the most damning point (for me) is the opacity of the system. Why x costs 3 and y costs 8 is not inherently clear (and in many cases isn't a coherent plan, just the result of playtesting). That makes statting up a lot of the Nightside really hard.
Now, this isn't a condemnation, and I'd bet money all of the info needed will be in the generic version of this edition of FATE, but it wasn't needed for this game and, that being the case, it's not here.
I'd absolutely use the DFRPG system unaltered for other urban fantasy (True Blood and the Mercy Thompson series by Patricia Briggs leap immediately to mind) but the Nightsde are EPIC!!! Urban Fantasy, with ebverything dialed up to ELEVEN!!1!!1 (And that, too, is not a condemnation, I love them for it) and that's outide the RPG's capabilities without so much house ruling you'd be better off using another system (adding Aspects to Mutants and Masterminds is pathetically easy and likely what I'd do).