Ok... hmm...
Well, I think I gotta say this: "No custom factions please!" and "No new factions please!"
If you can have this society be part of another faction, operating on it's own but still reporting to someone, then by all means go for it. But if you want to add a 16th faction into the mix... (12 humans + 2 aliens + 1 Planetmind + your guys = 16), I gotta draw the line.
Secret societies like the Apex Council are fine, becuase they can't really fight wars, have diplomacy, establish their own bases, etc. If that's similar to what you have in mind, then it's good. BUT, if you want to do the classic "break away and start my own colony" approach, I don't think so. 15 factions is already too many to follow, so we can't have new ones popping up left and right.
If that sounded redundant, it is because it was

. Anyway, if you can work it out, email Paul and I a copy and we'll look it over (any other writers can get a copy from us by asking)
Happy posting!
- Jasonian