Just for clarification the FW books are mentioned under the Campaigns section in the rulebook. Specifically page 383.
I have always found it dumb that people wouldn't allow FW and base it on the idea that it is unbalanced. I can see if you are using the rules that they release as experimental, but once they put out the Imperial Armour book, it should be enough. There was this complaint, but it is addressed in the official Apocalypse GW book, I believe in the introduction of the book.
I purchased a Nightwing when FW released it and it was a big issue with me using it. I could see back then because there were not really any flyers or the main rules didn't address them. But now, if you were to show up with one of the newer codex armies that each have two flyers in them, and you try to tell me that I couldn't take a Nightwing, I would laugh in your face and find someone else to play.
Times have changed, but this old attitude of FW being unbalanced or over powered still remains. If this is the case, then how can GW proclaim in the official 6th rulebook that the Badab Campaign rules are "arguably the ultimate campaign guides"?