Judging by what you have in quotes, his FOC re-structuring only affects the detachment Sammael is in. It says "In a primary detachment, etc." not "In an army, etc." The new Eldar codex says that you just need a Farseer in the army to make Wraithguard and Wraithblades Troops. An option for you, though, is to take Sammael in one detachment and Azrael in the other.
"Fetch me another plaything. This one seems to have broken." -Urien Rakarth
Space Marine- "This planet is ours, witch."
Eldar- "No ... This planet is theirs ..."