Will the UEE Security shoot at every Scythe at sight?

NO! Ship recognition is more complex than just according to silhouette. If you're broadcasting a Vanduul IFF signal, though, you might want to look out (this is a bad idea for most purposes.) Also be aware that this only applies to AI; it's certainly likely there will be players jumpy enough to shoot a Scythe on sight (try saying that three times fast.)