I would run full Special Attack EVs, personally.
Anyway, I've never seen a Flash Fire Ninetales, but I think it could still be viable.
If you use it in Doubles (replace Flamethrower with Heat Wave, maybe Disable with Protect), you can have a Pokemon with a Fire type move next to it. I would suggest Prankster Will-O-Wisp Sableye, since it can get a priority Will-O-Wisp onto Ninetales and then Ninetales could use Heat Wave after the boost.
Ninetales @ Sitrus Berry
Ability: Flash Fire
EVs: 252 SpA / 4 SpD / 252 Spe
Modest Nature
- Hex / Nasty Plot
- Will-O-Wisp
- Heat Wave
- Protect
Sableye @ (?)
Ability: Prankster
EVs: 252 HP / 128 Def / 128 SpD
Careful Nature
- Knock Off
- Will-O-Wisp
- Fake Out
- Recover
Hope this helps! :)