I guess the FW stuff will all be down to what it claims the codex "counts as" for the allies matrix.
If it says they are CSM then they would count as CSM for FW stuff. Same with Daemons and Daemon stuff.
Though if they have a unique one then it will not count as any (unless it states otherwise). Though I wouldn't begrudge anyone from taking Khorne or unaligned FW stuff that is Chaos as whatever slot it normally fits in. Though something like a Silver Tower or Tzeentch what is usable by CSM or Daemons I would not, as it is Tzeentch.