Look at the picture I posted. The Command Formation has a caviat saying he can replace the Tank Commander, the Armoured Company does not. I can post a bunch of other Formations that have similar restrictions on Unique Characters, but have done so several times at this point and am feeling lazy.
GW also has the Emperor's Fist boxed set pictured with 20 Guardsmen (instead of 50) saying that it's 'all you need' for that Formation, and Battlescribe is not a valid source for rules no matter how pretty the interface is.
Just confirmed with one of the guys who run the NOVA Open that he in fact can be. There are no restrictions on the formation. He's a main character in the Mont'ka book as well so it makes sense.
Not trying to argue but I believe you're mistaken mate.